91 Park Ave Rough Idle

[Rhysj]

I have a 1991 Park Ave 3.8L which has been pretty much sitting for two years. I have had to replace the ECM which let it start, and I've redone the Sparks, but I'm still having a real rough idle both cold and hot. All cylinders are firing, at least it gets rougher on all cyls if I pull the spark plug wire and I can attest to the fact that there is a good spark (ouch)! Seems to run fine under a load, but occasionally, there is a momentary dropout, and it bumps the tranny pretty hard...

Any ideas? ( I ain't no mekkanick, but I can foller instrukshuns!)

[tman]

My 94 was in the same situation, it sat without being started for 18 months. I've so far replaced the lower intake gaskets, rockerarm cover gaskets, tensioner pulley, spark plugs and wires, changed the transmission fluid. The more I drove the car, the better it seemed to drive. Now there is just a slight vibration it the gas pedal under gentle acceleration, but all in all, it seems to be getting better with time and driving. I am also having problems with my gas tank, you need to be sure that there is no water in your gas tank. I'd reccomend having you favorite GM dealer give the car a lookover before really driving it down the road fof any extended journey.

[Flatrater]

First thing to come to mind is stale gas!!! Two year old gas is not good for much but to run your lawnmower on!

Many other things can cause a rough idle!! Dirty IAC motor and throttle bore, vaccum leaks and so on. Best thing to do is take it to a good shop and have them scan it. Then they would reccomend needed repairs which more than likely you could do yourself. Let them do the hard work for you.

[Rhysj]

Thanks for the replies! I will let you know what I find out. It does seem to be smoothing out the more I drive it.

[tman]

Drive down the interstate for a half hour, then turn around and come back, dont use the cruise control, I did that a few times, and my car really straigtened up in a hurry!

[Rhysj]

OK, now I have a 21 and a 34 code. The MAF is clean and intact, throttle bore was clean as a whistle. I've heard that a clogged catalytic converter can cause this. What would be my next bext bet? Oxygen sensor coded out the other day, but after a reset, and two good hours of interstate driving, it has not resurfaced.

[itspaid4]

if you are still around, what did you find out on your 21 code. I have the same problem, have replaced the TPS.

[Rhysj]

I continued to drive it to work thru the winter (about 80 miles a day), and once it got cold, the engine light went out and never came back on, even though it's 90 degrees now...

Wish I could tell you why!

[itspaid4]

Thanks for the reply, did you check/change the air temp sensor that is located under the air cleaner-its a real easy test with an ohmeter and a hair dryer.
thanks again

[Rhysj]

I replaced it, I think you are talking about the one on the back side of the air cleaner? I changed it out because the external temp meter in the car shows 49 degrees no matter what. It still does, so I assume there is another one somewhere. I haven't traced the wires to be sure there is no break. Is that a "default" temp setting?

THanks!

[itspaid4]

i dont know what the default temp setting is but it sound to me like you are on the right track with the bad wire. maybe unplug the sensor and see what typre of reading you get.

[Rhysj]

The same temp reading. I haven't fooled with it for a while, due to lack of time, and the fact that I lost the transmission on it... (luck abounds!)

[Jed Rule]

The outside temp sensor is behind the grill. If you have access to a scanner, check that the air temp and coolant temp read the same after sitting overnite

[Hobiehunter]

I believe that if the battery was disconnected or dead for any length of time the computer ECM has to relearn so that it can make appropriate adjustments to timing,fuel... .

there may be a relearn procedure.

[Rhysj]

I've replaced the ECM since then, and I'll look for the temp sensor behind the grill as indicated! Thanks!