Engine Idle Issues + some

[J33ps]

Background:

 

A few months ago I noticed my AW4 tranny would not shift, it was stuck in 1/2.  I removed the fuse to the TCU and it shifts fine so it's a sensor problem.  So I went to Cruiser's tips and decided to clean the throttle body and sensors.  When I put it back together it started idling like crazy, it kept revving up then down then up and down constantly.  So I grabbed my meter and determined that my TPS is bad.  No problem, put a new TPS on it and measured and I got it close (how close to 17% does it need to be?).  Anyway it is idling BETTER than it was but it's still acting weird and now it's doing other weird stuff and idle still kinda sucks.  To be fair this engine has sounded funny since I bought the truck but I don't drive it in the winter so I have very little road time with it.

 

I'll try to be concise but I've never done engine work before, I'm learning as I go.  I have an 04 wrangler with a stock 4.0 in it.  It sounds like champ compared to my truck.  Here's what I was told from PO (I don't trust him):

 

Truck is supposed to be a 1990.  Engine in the truck is from a 1998 jeep cherokee XJ, it's a 4.0 (he says the AW4 tranny is from a 1988 XJ) the engine has old stuff on it and does not use the same parts as my 04 TJ.  I have a strong feeling it's more like a 1988 4.0 but I have no idea how to figure that out.  The throttle body and such is the old design as far as I can tell.

 

Symptoms:

1). Engine idles a little rough but not terrible, it revs up/down a bit

2). I can hear a very audible air leak

3). When I rev the engine it's not consistent, it even drops RPM randomly as I steadily give it gas

4). When I hit 3k RPM (it's parked, just sitting in the driveway) I can hear a THUMP THUMP THUMP and it won't go above 3k

5). VERY STRONG gas smell -- gas was last filled back in november (maybe it's old??), i rarely drove it through this winter to keep it out of the salt

6). AW4 won't shift at all -- this is what started my investigation, I'll deal with this once I get a happy idle and can rev smoothly

 

What I've Done:

 

I cleaned the throttle body and put it back together with a new gasket.  I replaced the TPS cause my meter said it was bad.  I put in a new one, adjusted, turned on the engine, it idled high, readjusted with engine running and it's spot on.  With the engine off it's reading a bit lower...idk if that's bad.  I needed 0.829 and with the engine running it's exactly that but with the engine off it's 0.821

 

Since it was having trouble I put in a "new" IAC but no difference.  Truck came with a bunch of parts, I'm just throwing them on lol.

 

I don't really know what I'm doing   I took some videos for audio purposes, maybe I could get those up.  I'll see if they'll upload from my phone later today.

 

[fiatslug87]

Here’s how you can tell the year of the engine block. 

[89 MJ]

It shouldn't really matter if the 4.0 is from an 88 or a 98. You could quickly look towards the rear on the driver side of the cylinder head next to the valve cover and know what the cylinder head is from, which would probably mean the engine is the same vintage. Somewhere there is a date code cast into the block too, but that's not as easy to find. The Renix (87-90) head is 2686, the OBDI HO (91-95) head is 7120, the early OBDII HO (96-98, IIRC) head is 0630, and the 99-01s used the 0331 head. Here is as thread on identifying the engine year:

 

Renix is not as smooth as the later fuel injection systems, in my experience. It is a very early EFI system, but it does sound like you've got some issues. The audible air leak needs to be found and fixed, that is likely a large portion of your issue. How clean is your new IAC?

[J33ps]

Thanks guys!  So I did do a quick search and sure enough it has a 0630 head so it must be the 98.  Thing that throws me is I bought a water pump for a 98 but it didn't fit.  Had to go with a different one.  Maybe just bad part labeling who knows.  As for the IAC I have like 3-4 that look clean, possibly never used.  The one installed I cleaned up real good with the whole throttle body but I thought maybe I was too rough with it and swapped it out.

 

I've decided to make sure the entire vaccuum system is solid.  I noticed a few dry rotted hoses on my system.  I'm going to start there and make sure it's fully sealed up before moving on.  Sounds like a tea kettle lol.

 

Also, during my testing yesterday I noticed it is now sputtering some oil through the exhaust.  It's still on my driveway today lol.  What causes that?  Are those bad CCV elbows?

[llhat]

liquid oil or blue oil smoke?

 

valid thought on getting those vacuum leaks stopped.

 

this sounds like a long path, but navigable

[J33ps]

21 minutes ago, llhat said:

liquid oil or blue oil smoke?

 

valid thought on getting those vacuum leaks stopped.

 

this sounds like a long path, but navigable

Agreed, I think it's going to be a nightmare but going to spend some time learning how it works before I start tearing into it lol.  It spit out liquid oil.  I do not (luckily) see or smell any evidence of burning oil.

[J33ps]

Well I’m embarrassed but I’ll say it anyway…I had forgotten to plug the map sensor airline back up to the throttle body.  Now it runs much much better.  
 

But in my search i did come across a part that has 2 hoses that are rotted and not hooked up.  What does this do?  It says carb bowl.  One hose runs to the air box and the other down under the jeep.  My first thought is….gas tank purge??

[llhat]

yes, charcoal canister for evap system... at some point in running cycle, there will be a vacuum signal to purge the vapors,

believe controlled by a solenoid on the drivers side fender...  not sure where a vacuum diagram is posted .

 

I'd either cap them off or (preferred) fix them.  one of course goes to top of fuel tank, there's probably two fittings on top of tank "Y"d together for trip to canister.

 

yep, not having the map sensor detecting vacuum will do some funky things...

 

sill have marginal concerns with liquid oil  from exhaust...  sure not condensation with carbon/oil mix ?

[J33ps]

1 hour ago, llhat said:

yes, charcoal canister for evap system... at some point in running cycle, there will be a vacuum signal to purge the vapors,

believe controlled by a solenoid on the drivers side fender...  not sure where a vacuum diagram is posted .

 

I'd either cap them off or (preferred) fix them.  one of course goes to top of fuel tank, there's probably two fittings on top of tank "Y"d together for trip to canister.

 

yep, not having the map sensor detecting vacuum will do some funky things...

 

sill have marginal concerns with liquid oil  from exhaust...  sure not condensation with carbon/oil mix ?

 

I can fix em, just need to cut and extend with some new hose.  I thought the charcoal canister was under the truck next to the gas tank.

 

I took it for a test drive today, getting that TPS replaced and dialed in fixed my AW4 shifting!  It was a nice little drive.  I have not seen any spitting of oil this time.  It's been sitting a while all winter, you may be right and it's just some gunk formed over some time.  I'll keep an eye on it.

[llhat]

sounds like really good news.

the shifting issue being fixed was an added benefit,  but the inputs from the TPS are also 'part of the plan' for the TCU,  mine was not as simple.

 

good luck with the rest and enjoy the drive..

[pizzaman09]

While you are at it, it is worth checking to see if your intake and exhaust header bolts are tight at the head.  They like to come loose on these engines and you end up with some of the symptoms you list.

[AnotherOldJeepGuy]

Some of my recent learning experience here which includes some pics that helped me locate and eventually check/tighten the manifold bolts...