TPS or AIC?

[clinck]

Lately My 99 GC (4.7 liter, 92,000 miles) has been idling a little rough when stopped at stop lights or just sitting in one spot idling.

When sitting and idling the RPM's will drop by 100-200 or so, just enough to feel like its is going to die but always recovers. Some days are worse than others. Driving down the road it doesn't have any problems.

A couple months ago I replaced the crankshaft position sensor to fix other rough idling that was much worse than now, so I dont think it is that unless the sensor went bad for some reason. The throttle body was cleaned recently by the dealer and it seemed to start after this.

Anyway, I am wondering if the TPS or AIC might be that cause of this and which one might need replaced.

[mx52nv]

clean your IAC first, then test your TPS. if they cleaned the TB, it may have gotten some of the gunk up in the IAC.

[clinck]

Can do, but how do I test the TPS? Just run the jeep and see if its any better or is there some real test for that?

[carlos80]

the most you can do without a scanner or oscilloscope is to check the voltage going to the tps(vref), it's minimum voltage signal(at idle) and it's
maximum(WOT) with a multimeter. another thing that i would recommend is checking for vaccum leaks unmetered air getting to your cylinders can cause the symptom you describe. you can chesk for leaks by using a water bottle and spraying areas where you might think a leak can occur. if you see a change in the vehicle idle when you spray a certain part then you've got your leak. good luck

[glennco1]

Chrysler has issued a TSB regarding rough idle while warm on all 4.7L WJs. The solution was to do a flash upgrade to the PCM

[glennco1]

My bad, I looked this up and the TSB only encompasses 02-04 model year 4.7 l

[dksob81]

TPS TEST........ get a DVOM, backprobe the Center wire (on the TPS) with the Positive Lead, then place the Negative Lead on a good engine ground (NEGATIVE BATTERY TERMINAL). Turn the Key to the "ON" Position, the TPS should be between .20v and .90v (@ Idle) slowly open the throttle - the Voltage should increase smoothly to 4.5v @ Wide-Open Throttle.

[clinck]

Originally Posted by glennco1

TPS TEST........ get a DVOM, backprobe the Center wire (on the TPS) with the Positive Lead, then place the Negative Lead on a good engine ground (NEGATIVE BATTERY TERMINAL). Turn the Key to the "ON" Position, the TPS should be between .20v and .90v (@ Idle) slowly open the throttle - the Voltage should increase smoothly to 4.5v @ Wide-Open Throttle.

Ok, Finally got around to doing this. At closed throttle I had .63v and at open throttle I had 3.78v with good smooth stepping through movement. I dont know what the tolerance is (3.78v close enough to 4.5v?) so I dont know exactly if the TPS is bad or not.

Since I posted this the problem seems to be getting worse (After warmup 5-10 minutes) I sometimes now will have sputtering (rough engine running) when accelerating from a stop.

[dksob81]

I don't know what the tolerences either, when I tested mine awhile back, I got the same exact reading of 3.78v.. so I waited and someone else had just replaced theirs and I asked them to test it and he said the old on was righ at 3.75v and the new one was right on the money of 4.5v, so I decided to replace mine, the new one i got I tested .63v (@ idle) and 3.88v (WOT). So I'm not sure anymore either. I did not have any acceleration problem or anything like that, I was just going through, I had a starting issue and was testing the IAC at the time and decided to check the TPS while I was at it.

I might replace the TPS again, the last one was a WELLS brand from autozone - and autozone isn't too reliable on the quality end of things.

[clinck]

Well my problem got worse last week and with the Voltage on the TPS not quite up to par I (and it being the cheaper between TPS or IAC) I replace it. High voltage was up in the 4's now instead of 3.78. Dont know exaclty because of the volt meter I had on hand. As soon as I started the engine with the new TPS it definately had a hard time staying running for the first 45 seconds or so as it was correcting itself to the new TPS. I thought mabey this would finally be be end of my problem.

Well later that day when I went out It was still idling rough and rough going from a stop most of the time. On Saturday I got the check engine light and was saying to myself "Great! Now it will tell me what exactly to look at". P0303 error wich I saw before and remembered being Cylinder #3 misfire detected. So I ended up taking it back in yesterday (tuesday) because this is somethign they were supposed to fix when they had it couple/few weeks ago. They ended up this morning finding a bad coil on Cylinder #3 and replaced it. I just picked it up and it is running much much better.

Just wanted to give an update for others that may run into the same thing.