View Full Version : Anyone heard of this?

05-07-08, 12:10 PM
:canttalk: This is a subject that should get its own forum... Ok, 98 deville 4.6. I cleaned the IAC, no change in intermittent fast idle. So I buy a new one for 82$. Good for awhile(hours). Next day ran with ac and was happening often. I can shut off car cycle ign switch 3 times and it fixes it for the moment. By the way, how does this work?
So its still doing hte same thing and i read on here how to clean egr and Ill try that but really im ready to buy whatever and replace it if i knew what would fix it! I thought I read something about a TP sensor but i couldnt find it in searches or the location of it...
Will someone please tell me what to buy and or clean and where it is located so i can drive a safer car... Other that pulling off the interstate at a stop light and slowly getting the car stopped with the engine fighting, I love this car! Most comfy car Ive ever had. Plus, i dont want my wife driving it if its goin to kill her... no life insurance on her yet. JK:stirpot:
Please help struggling stay at home dad out...lol

05-07-08, 05:27 PM
Pull codes first:


05-07-08, 08:52 PM
After you pull the codes, I'd start with a good TB cleaning. Then the EGR valve.

How does what work? The IAC valve? The throttle plate is closed at idle, unlike some other engines or earlier versions of the Northstar that keep the throttle plate cracked open to idle. To prevent the engine from dying, there is an air bypass circuit around the closed throttle plate. The IAC valve controls how much air bypasses the closed throttle plate to control idle speed.

05-08-08, 07:33 AM
Thanks chubby and ranger. I was wondering about the ign trick ranger. But ive pulled the codes several times while it is idleing fast and there is never anythign current but the 0741 or whatever that torque converter thing is. Unless the egr valve is over 100 bucks ild almost rather just replace it than remove fuel rails and all that more than once if it can also fix the fast idle... I also read on here something about holding the pedal WOT and turning the key on to have the pc relearn the throttle but it starts everytime so it must be for newer cars that it wont start with WOT. Do you think I should also do anything with the TP sensor? seems like this is never a cut and dry problem or fix...:banghead:

05-08-08, 11:29 AM
What ignition trick?

Holding the pedal at WOT during cranking places the engine in clear flood mode (shuts of the injectors).

I would not replace the TPS.

Did you clean the TB?

El Don Oso
05-08-08, 06:32 PM
If the throttle body is clean and the accelerator cable linkage is free on not sticking. Then yeah the TPS (throttle position sensor) would be the next thing to check. That’s its function is to regulate the throttle and the amount of air intake. The TPS is located on the side of the throttle body towards the front of the car.

05-08-08, 08:47 PM
The TPS does not regulate anything. It tells the PCM what position the throttle is in so that it can determine the correct pulse width to the injectors.

05-08-08, 10:36 PM
It could be a TPS with a dead spot. There is a feature called the "throttle follower" that opens the IAC as the throttle is opened. This is such that if the driver applies and suddenly releases the throttle, the engine won't stall. This is particularly important close to idle and low speed conditions. Since the IAC isn't the culprit, and it is still increasing the idle beyond where it should be, then the PCM must think that it's NOT idle and the driver is moving the throttle off the stop. The TPS style the N* uses is common to most 90's GM cars. You can probably pull one off at a junkyard for $5.

The computer is usually very good at finding bad TPS', though they can sometimes sneak by if they go bad after the engine's running. (e.g. a dead spot that only appears after it gets hot)

05-08-08, 11:27 PM
I went to the parts store to price a EGR and DANG, I was surprised to hear 179.00. It seems like if I run the AC it is def. goin to idle high. I still have yet to try and clean the egr and spray in the TB. I read the one post on how to clean the egr and it seemed like all you could really clean was the face of the valve and that button thats suppose to move. Apparently your not suppose to get the currosive cleaner inside the valve. I guess i dont get how effective that could be when you cant clean it much.
I guess i didnt look very well but i didnt notice and sensor on the same side as the AIC. So i dont know where the TP is. And i guess the tp is not somethign i can clean. I wonder how expensive that would be to replace??? So ill keep tryin! It seems like it would be the computer if i can cycle the ign switch and it fixes the high idle every time even if it is for a short time....:hmm:

05-09-08, 12:10 AM
It's right below the IAC on the same side. I think generic ones are about $20, Delco ones about $40.

05-09-08, 11:30 AM
The TPS is inline with the throttle plate fulcrum.

El Don Oso
05-13-08, 12:11 AM
So my description of its function was a little off. But that doesn't limit the fact that if the TPS is malfunctioning it will effect the idle and should be looked into.