Engine Idle quesion... (IAC, MAP, TPS, Temp units)

[skidoo_j]

Please Read entire scenario Prior to comment THX.

 

I have an 89 4.0 comanche with 129k I recently put the dynomax headers on. When I did this I also removed the EGR valve from the header and replaced with a 1/4" plate. I also plugged the egr tube ext on the exhaust and on the intake. removed vacuum and plugged lines to egr and air box. also installed a new o2 sensor by bosch.

 

So here's my question... When i start the truck from cold (or rest for 15 min or more) it will run at 1100 rpm and drop pretty fast to 700 ish rpm's. and will stay at this idle speed for extended periods. I've even created a vacuum leak and then plugged and it will return to this speed. According to the FSM It appears this is with in spec.

 

However when i drive the truck around and pull up to stop or park in the garage the truck will not come down off of 1100 rpm unless I strain the motor (hold brake and let off clutch). then it will idle at 700 ish rpm.

 

since i've noticed this problem (very plausible existed prior to install of header) I have:

Plugged vacuum that controls heater vlv at the manifold.

removed the Idle air controller and cleaned the pintle and throttle body seat (was nasty)

cleaned entire throttle body.

replaced oil fill cap w/ new

inspected all throttle cable linkage.

used propane / starting fluid / and wd40 searching for vacuum leaks at this high idle.... three different times. around rusy's tb spacer and all intake ports i can get access to.

 

 

Is this normal behavior with our renix type systems? My VW GTi does this but the ecu has sensors for speed and keeps engine rpm higher than idle until at complete stop for a minute or so to prevent me from coasting and then putting in gear at low engine rpm while going 60 mph. I could not find any such sensor in the fsm except the CPS but that monitors crank rotations not vehicle speed.

 

The Jeep will not come down off this 1100 rpm like i said unless i strain the motor.

 

I"ve also previously adjusted the Throttle position sensor according to factory. but did not replace.

 

I'm just kinda lost at a potential cause for this issue unless it's normal behavior as vacuum is kinda hard to believe as a cause because straining the motor should not create or eliminate a vacuum leak to drop it down hence why i think it's electrical but ???

[skidoo_j]

57 views and no response??? I've stumped you guys too?

 

:???:

[skidoo_j]

Well due to lack of response I've started on another guess and check... Today while the truck was stuck on high idle i adjusted the throttle stop screw until it was at 550 rpm.

 

Now I'll see if when it used to come down to that area it just dies or ????

[Boots]

Try cleaning the IAC it's on the left of the TPS.

[cruiser54]

Tutn the throttle stop screw back in until the butterfly just starts to move. That's where it needs to be to keep the butterfly from digging into the walls of the throttle body itself.

 

Then, adjust your TPS. Good possibility it's bad and that's what's causing the idle to hang.

 

RENIX TPS ADJUSTMENT

 

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.

It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

 

IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector

of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post.

If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be

necessary. The harness repair must be performed before proceeding.

I can provide an instruction sheet for that if needed.

 

MANUAL TRANSMISSION:

 

RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.

This manual transmission vehicle TPS provides data input to the ECU. The manual transmission

TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.

 

Wire "A" is positive.

Wire "B" is ground.

 

Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..

Note the voltage reading--this is your REFERENCE voltage.

 

Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your

OUTPUT voltage.

Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For

example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If

you can't achieve the correct output voltage replace the TPS and start over.

 

AUTOMATIC TRANSMISSION:

 

RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-

wire connector, same as the manual transmission vehicles have, and it is tested the same as the

manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.

 

However, the automatic TPS also has a square four-wire connector clearly embossed with the letters

A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.

 

Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your

REFERENCE voltage.

 

Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT

voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.

For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.

If you can't, replace the TPS and start over.

 

So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and

the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire

connector side of the TPS. If you have ENGINE issues check the three-wire connector side of

the TPS.

 

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is

stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

 

Revised 11-28-2011

[skidoo_j]

Try cleaning the IAC it's on the left of the TPS.

 

Thanks for the suggestion, however I'd already cleaned the Idle Air Controller pintle and seat

[skidoo_j]

Tutn the throttle stop screw back in until the butterfly just starts to move. That's where it needs to be to keep the butterfly from digging into the walls of the throttle body itself.

 

Then, adjust your TPS. Good possibility it's bad and that's what's causing the idle to hang.

 

RENIX TPS ADJUSTMENT

 

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.

It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

 

 

This is a much better procedure than what I have in my service manual. Mine said to just adjust it to .85 volts. I didnt agree with it because the alternator could have pulsed it. I will go adjust it using the 17% rule. Will post how it goes. thx :wrench:

[cruiser54]

Be sure to set that throttle stop screw where it belongs first.

[skidoo_j]

Touch the black lead of your meter to the negative battery post.

If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be

necessary. The harness repair must be performed before proceeding.

I can provide an instruction sheet for that if needed.

 

My meter read 10 ohms to negative when the connector was plugged into the tps. I was thinking the 10 ohms could have been from the back feed. When I measure impedance with it unplugged b-neg was 0 Ohms.

 

To modify the ground you're suggesting to just splice wire to ground? As my my reading would already indicate I had good ground on the wire with 0 ohms when unplugged.

 

 

I did change my tps to 17% of 4.85v without altering the wiring.

 

I set the butterfly stop about 1/4 turn past where it looked as if the flap touched.

 

And I'm still receiving the same behavior. I did also check voltage from a-b b-c comparing to a-neg neg-c. The voltages were the same with in the accuracy of my meter.

 

 

Symptom is:

Start truck. runs around 1200 rpm... idle drops to 600 rpm area rapidly.

 

drive truck, stop at light 1100 rpm, drive stop at sign 1200rpm... come back to house idle 1100 rpm. let sit for 2 min still 1100 rpm. rev rev idle drops to 1000 rpm (sometimes reving it brings it to 600rpm range).. clutch in first gear clutch out while holding brake but not let die. idle drops to 600 rpm.

 

 

 

I've wanted to test the IAC motor, but I don't have a voltage stepper as described in the manual to test it. Any ideas as to what could be used?

[skidoo_j]

I got it to stick at 1100 rpm with out driving... engine was warm... could not get it to drop by either creating vacuum leak or unpluging iac or reving motor... had to strain motor.

 

 

measured map output at 600rpm is 1.20v (fsm says should be 1.5v) ISSUE?

 

measuring resistance across tps as move flapper appears very consistent.

 

measured resistance across iac out side two 55ohm inside two 56 ohms

 

7 ohms at o2 sensor...

 

both engine coolant temp sensor and manifold air temp are in spec at current temp...

 

 

 

still thinking iac... maybe map or ecu...

[skidoo_j]

also found that if stuck at 1100 rpm and unplug iac i cannot get it to come down at all...

 

Does this imply the iac is working?

when at 600rpm and turning wheel allway to one side or other idle does not increase, it decreases

[cruiser54]

Touch the black lead of your meter to the negative battery post.

If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be

necessary. The harness repair must be performed before proceeding.

I can provide an instruction sheet for that if needed.

 

My meter read 10 ohms to negative when the connector was plugged into the tps. I was thinking the 10 ohms could have been from the back feed. When I measure impedance with it unplugged b-neg was 0 Ohms.

 

To modify the ground you're suggesting to just splice wire to ground? As my my reading would already indicate I had good ground on the wire with 0 ohms when unplugged.

 

 

I did change my tps to 17% of 4.85v without altering the wiring.

 

I set the butterfly stop about 1/4 turn past where it looked as if the flap touched.

 

And I'm still receiving the same behavior. I did also check voltage from a-b b-c comparing to a-neg neg-c. The voltages were the same with in the accuracy of my meter.

 

 

Symptom is:

Start truck. runs around 1200 rpm... idle drops to 600 rpm area rapidly.

 

drive truck, stop at light 1100 rpm, drive stop at sign 1200rpm... come back to house idle 1100 rpm. let sit for 2 min still 1100 rpm. rev rev idle drops to 1000 rpm (sometimes reving it brings it to 600rpm range).. clutch in first gear clutch out while holding brake but not let die. idle drops to 600 rpm.

 

 

 

I've wanted to test the IAC motor, but I don't have a voltage stepper as described in the manual to test it. Any ideas as to what could be used?

 

 

Did you test the sensor ground circuit resistance with the key on or off?

 

Perhaps a 1/4 turn AFTER the butterfly starts to move is too much. It's just a stop, not an idle setting.

[skidoo_j]

Did you test the sensor ground circuit resistance with the key on or off?

 

Perhaps a 1/4 turn AFTER the butterfly starts to move is too much. It's just a stop, not an idle setting.

 

Key was on when i got the 10 ohms with connector plugged in.

 

unplugged 0.3 ohms with key off

plugged in 0.4 ohms with key off.

 

 

I adjusted the butterfly again until there was just enough tension to hold a piece of paper between the stop and lever.

[skidoo_j]

While talking with someone regarding this issue I stated i was wondering if my ECU was toast. They then asked if I had welded on the truck.

 

I have. When I replaced the floor pan in the truck we did not disconnect the battery. He then told me the ECU was toast. Would there be any validity to this? The truck seems to run perfectly except for this idle issue.

 

well and i'm getting what i think is lower than normal mpg 14.5 but there are some other things i think maybe causeing this as i'm carrying a couple sand bags and have been hauling the motorcycle to and fro the mtn. Tomorrow I will drive 60 miles with out stops so i will know if having issues with fuel mapping across board.

[carnuck]

Try unplugging the iac after you get the RPM down to near normal.

[skidoo_j]

Try unplugging the iac after you get the RPM down to near normal.

 

I had not though of running the truck with the iac disconnected. I figured it would move by vibrations, but it may provide me with a better guess if the iac is bad or if the map is bad.

 

 

With IAC unplugged running/driving senario:

 

I started truck and waited until it came down to 600 rpms then unplugged the iac.

shut truck off. waited 10 min and started it. It didnt want to run much but chugged its way to 600 rpm. I drove 12 miles and it was stuck at 1100 rpm area. tried bogging engine, reving the engine, removed vacuum hose idle went up reconnected 1100 rpm.

 

reconnected iac few seconds and it went down to 700 rpm.

[skidoo_j]

second run. i turned ignition on, turned off, disconnected iac. then started truck 2k drove down road 2k. stopped 2k got out connected iac 1k...

 

So it appears the IAC is not totally bad, and obviously it is capable to bring the idle down....

 

Ideas thoughts???

[carnuck]

Could be the IAC is going bad

[skidoo_j]

replaced the map sensor. Idle will now drop to 400-500 range.

 

the truck's idle will still hang a little high, now at 1000 rpm, however it's about half as frequent.

 

it also takes a lot less to drop the idle, before it would take a hard strain on the motor and a cycle of slipping the clutch etc now just an instant of stain and drop.

 

I do think the iac maybe having some issues though because the idle dropped so low at one point it then picked up to about 700 rpm like a anti diesel effect kicked in.

 

i may pull the iac again and clean it a second time. I would love if napa or autozone would let me "try" a new one. I just don't want to spend 100 on one and it make no difference.

 

the map at $30 is bad enough.

[skidoo_j]

Well for about a week i thought i had it fixed... During this week i only drove mostly short trips. Today i drove 10 miles on freeway and it's acting exactly the same.

 

500 rpm idle after start settles

1100 rpm idle when just to a stop from driving

 

hard to get drop lower that 1000 rpm.

 

 

 

ANY IDEAS??? Was thinking maybe the IAC is bad/going or has a bad spot on the pintle. I'm going to go pull it again and clean it this evening. PLEASE help.

[skidoo_j]

Okay so I pulled the IAC and there was a pretty good rub mark from where it looks like maybe the pintle is out of alignment and pushes up into the seat.

 

The pintle has play about 1/8" in rotation.

The pintle shaft has side to side play. (as in it can Rock side to side)

the pintle and shaft would not push in or out.

[cruiser54]

Check your TPS on the "engine side" per the instructions:

 

RENIX TPS ADJUSTMENT

 

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.

It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

 

IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector

of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post.

If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be

necessary. The harness repair must be performed before proceeding.

I can provide an instruction sheet for that if needed.

 

MANUAL TRANSMISSION:

 

RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.

This manual transmission vehicle TPS provides data input to the ECU. The manual transmission

TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.

 

Wire "A" is positive.

Wire "B" is ground.

 

Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..

Note the voltage reading--this is your REFERENCE voltage.

 

Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your

OUTPUT voltage.

Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For

example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If

you can't achieve the correct output voltage replace the TPS and start over.

 

AUTOMATIC TRANSMISSION:

 

RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-

wire connector, same as the manual transmission vehicles have, and it is tested the same as the

manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.

 

However, the automatic TPS also has a square four-wire connector clearly embossed with the letters

A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.

 

Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your

REFERENCE voltage.

 

Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT

voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.

For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.

If you can't, replace the TPS and start over.

 

So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and

the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire

connector side of the TPS. If you have ENGINE issues check the three-wire connector side of

the TPS.

 

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is

stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

 

Revised 11-28-2011

[skidoo_j]

Check your TPS on the "engine side" per the instructions:

 

 

followed them two plus weeks ago when you posted last time, but thanks for responding. any other ideas?

[skidoo_j]

Okay I'm still having the issue. I've replaced the IAC with one from a jy to no avail... about a week of driving and no improvement...

So, I've now replaced all of the following with new sensors that I tested before install. All temp sensors were with in 10 ohms :).

O2, Map, Coolant temp sensor, coolant temp sender, MAT, knock sensor, crank position sensor.

 

even with all of those sensors replaced, (all grounds test .04 ohms with key off) i'm still having issues.

I have given up and ordered a new IAC and throttle sensor.. When ordering these through autozone I found they have dramatic price regions. When using my zip code and in store they wanted 89 dollars for the IAC, I had entered my brothers zip in Beaverton, Oregon when doing part availablitly for him over the phone and didn't change it when I went to place the order and it was $60. Same for the TPS sensor.

 

While I'm waiting for those to arrive I decided to install the new rebuilt injectors that have been on my self for 4 months. I put 500 miles on all the sensors and was getting 17 mpg empty on hwy... so it's improved some. But like i said idle still hangs when coming down when stopped. Hoping the injectors improve mpg. Plan to put a few gas tanks through prior to installing the IAC and TPS.

 

Right now I doubt the IAC and TPS are the problem. It's gonna end up being the vent line between the gas tank and charcoal filter is broken and that's what is causing it.

 

 

anyone have a lead on the vacuum hose from the throttle body to the MAP. I've tried to check for vacuum leaks again with propane and no idle increase. Although i'm only checking vacuum to fuel rail, map and to valve cover. all others have been plugged. I did test all plugs.. and around all gaskets on the throttle body and my egr block plate.

 

 

Edited to correct an "auto spell correct" by google chrome

[cruiser54]

You haven't ever replaced the TPS, right?