What should I check first? I Live in Phoenix so it never gets cold but as the temp has gradually dropped to high 50's in the morning I seem to have a gradually worsening cold idle problem. Starts fine but runs high then falls to zero over and over. I can keep it running by feathing the throttle and after it warms up a little bit it runs fine. No codes, no engine light. Tested the IAC per the instructions and it checks out electrically and was very clean. Went ahead and sprayed some carb cleaner in it just to be sure but no carbon deposits at all. Will have to wait till the AM to see if it had any effect. I have tried to search for the thread on intake manifold o ring seals and can't seem to pull it up, after reading several idle problem threads it looks like that is a possiblity. Any other sensors that could cause this problem without throwing a hard code? Should I just pay the $80 to have it checked by a shop when cold to see if it gives a code while not running right?

 

You should be able to get it by any parts store to check things out for free.

Check the basics. Fuel pressure, air filter, check all the harness connectors (are they on tight?), PCV valve, check the hoses for cracks....all this assumes the IAC is 100% not the issue, but good to check for anyway.

 

See same thread under the 4.0 SOHC engine forum

 

Clean throtle plate.
Coolant temp sensor should throw a signal but it sure sounds suspect....it is temp related.

 

Bob brought his rig by today and well by the time he got here it was warm so we could not duplicate his cold engine eradic idel condition. Stored codes of p0171, p0174 said both banks looked lean. pull ed 2 plugs on drivers side, one on passenger. All looked OK with the one passenger looking a little leaner, whiter. All were pretty warn though and with 46K, well time for new plugs anyway.

Check the MAF sensor and it is deninitely dirty but of course I was out of carb cleaner. Tossed the sequrity torx bolts for socket head cap screws - Bob, I might have left the old screws on top of your radiator plastic plate thingy - you know where the tools go when you're wrenching. Anyway Bob's going to clean that and see if it helps.

I think the dirty MAF is running it too lean and at idle, with no O2's to help correct, it runs crappy.

We checked the TPS and it ramps up nice and easy to 93% open, per my scanner - I guess that's ~4.8V.

R & L O2's were switching OK and the short term A/F trim was going +/- so it looks like the O2's are working OK. The long term A/F trim looked + at 4-7% so that verifies the PCM really thinks the motor is a little lean.

Bob - since I forgot to clear the codes, you can disconnect the battery if you want and we can see if they come back. But once you clean the MAF sensor, disconnect the battery for sure for 10 min's to make sure those trim tables are zeroed out. If you don't do this the long term trm's could affect the performance for a while untill the PCM is relearned. fastest road to seeing results from a change you make is to clear the KAM by disconnecting the battery. After all this, we can scan it again and see if it looks OK. Of course, if the cold idle problem goes away who really cares right?

 

Oh yeah. After trying to remove plugs from a SOHC 4.0 - glad I'm not you guys! This job sucks! Working on my 93 4.0 is more like the motor is sitting in the garage on an engine stand. That much night and day difference. Now I see what ya'll have been talking about.

 

So Bob - what happened? Did cleaning the MAF and new plugs fix it?

 

No, changed all but 2 hardest to-get-to plugs, cleaned MAS, checked ohms on coolant temp sensor, no change in cold start idle fluctuation. Haven't had time to do remaining 2 plugs or anything else. Coolant temp sensor resistance was off about 20%, but changed consistently with rising engine temp. May have been do to length of wire I used to reach it because I didn't remove upper intake manifold and/or throttle body to get at it directly

 

Maybe see if the dealer can give any advice when they do the timing chain. If you disconnect the battery, we can always go back and revarify the codes.

 

Check the intake manifold gaskets they are little rubber o-rings as they get older they shrink and as the temps get colder the plastic manifold shrinks causing air leaks.
Also look for any vacum leaks

Been there before
Rich

 

FortyFord - he's got that on the dealer list as part of the timing chain.

 

I'm betting on the intake gaskets.

Mine does the same thing but doesn't start until it gets down into the 30's. I've checked everything and now I'm down to the gaskets myself. Hopefully I'll get those replaced in the next few weeks.

Anybody do that before - how difficult are they to get to?

 

Okay I didn't read the other post in the engine forum sorry.
Rich

 

oh yeah - I forgot he posted this twice. May be I should read that on too.