Idle problem. (not me- the truck)

[ChiefJosh]

I've got a problem with the idle on my Four-Oh. It seems to idle normally (around 750-850 rpms) when I initially start it in the morning, but as it warms up, the idle goes up. It's been around 25-30 degrees outside in the morning, so it's a bit chilly out. As the truck reaches operating temperature, it will settle in anywhere between 1750 to 2250 rpms! I feel kind of stupid sitting at a stop light with my engine screaming. Today I cleaned out my throttle body with some TB cleaner, and it seemed to make the problem worse. I have no idea what is going on- any ideas?

[Duner]

My 4.0 litre started doing this with the first cold snap this year. It seems to have improved some now stays around 1100 to 1200 rpm dropping back to normal sometimes. I suspect it is related to a temp sensor that is feeding info back to the injection circuit. Nothing like being stopped in traffic with your engine running 2200 and the clutch throw out bearing squealing as well.

 

Does anybody have the answer to this problem, I don't want to just randomly replace sensors.

[Eagle]

Throttle position sensor (TPS) and/or idle air controller (IAC) dirty. Cleaning might do it, but replacement may be in your future.

[ChiefJosh]

That's helpful, a starting point at any rate. My temp gauge is not functioning either, does the ECU accept any info from that sensor? Could that be related?

[87manche]

start here.

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

let us know what you find.

[Oizarod115]

check and make sure the vacuum lines are all connected, the vacuum line on the cylinder head of mine pulled out once and it idled ~1500

 

but that would be ALL the time, not just in the am.

[carnuck]

Make sure the hose that comes off the intake to the vacuum bottle isn't split. If you are having heat/defrost control issues and have a big dent in the passenger's side of your bumper, then the vacuum bottle is likely cracked (That's where they live stock. I replaced mine with a universal ball and put it under the hood)

The next thing to do is take a can of good throttle body cleaner (be careful to make sure that if it says "carb cleaner" that it is O2 sensor safe! Too many of my customers have had to replace recently changed O2 sensors because they used the wrong thing. WD40 is even worse because it is pure poison to O2 sensors!) and find the small idle air hole on top of the throttle body. Spray all the way around inside the main body to clean it, then put a "spoonful" into the idle port (IAC) and let it sit for a bit before starting.

Last, but definitely not least, is to take apart and spray ALL underhood connections with electrical contact cleaner/anti-corrode.

[Oizarod115]

Make sure the hose that comes off the intake to the vacuum bottle isn't split. If you are having heat/defrost control issues and have a big dent in the passenger's side of your bumper, then the vacuum bottle is likely cracked (That's where they live stock. I replaced mine with a universal ball and put it under the hood)

The next thing to do is take a can of good throttle body cleaner (be careful to make sure that if it says "carb cleaner" that it is O2 sensor safe! Too many of my customers have had to replace recently changed O2 sensors because they used the wrong thing. WD40 is even worse because it is pure poison to O2 sensors!) and find the small idle air hole on top of the throttle body. Spray all the way around inside the main body to clean it, then put a "spoonful" into the idle port (IAC) and let it sit for a bit before starting.

Last, but definitely not least, is to take apart and spray ALL underhood connections with electrical contact cleaner/anti-corrode.

 

sure is nice having a jeep mech. sittin around aint it boys? :brows:

 

keep on! (jeep on)

[carnuck]

When I can get over here. Days off are usually busy. Went to the dentist yesterday and the stuff they inject makes me feel like crap for a couple days.

[Eagle]

That's helpful, a starting point at any rate. My temp gauge is not functioning either, does the ECU accept any info from that sensor? Could that be related?

Not on an '88. The Renix system uses a dedicated sensor in the back corner of the head for the temp gauge, and a separate sensor down on the left (driver's) side of the block to feed the ECU.

[ChiefJosh]

Well, i took a look at the vacuum canister, and it looks okay, but I did replace the bumper after the guy I bought my MJ from had a close encounter with a guardrail. The idle wasn't really giving me problems until this past week, at least nothing of this magnitude, so who knows. I also know that the guy I bought the truck from only put on about 1000 miles in the past year, out of the 172,000 that are on the truck, so I'm sure it is still gettin used to being driven on a regular basis. I'll try the TB cleaner in the IAC bowl (I assume that is the roughly triangle shaped orfice on the top of the TB?), and see what happens. I'll also double check the ball while it's running.