RPM Variations

[old man]

Today, I was driving a passanger who does not like to go fast, I was babying the crap out of the car. We arrived at our destination, 73 approx miles, and went to pull in and pushed the clutch in. The RPMs stayed at 2000. Then, after about 30 seconds, went to about 1500 and then fluctuated between 1500 and 800 in a constant fashion. So I got home, and still doing the same thing. I Checked for vacuum leaks, found none. Did not show overheating. Seemed to drive fine. Left it sit for 5 minutes, it seemed normal. Then took it out and beat the snot out of it. No acceleration problems, no serging going down the road. Now when I stop at a red light, push clutch in and it says around 1500 then slowly drops. Recently had the same problem with my wifes 2003 Dodge Dakota 4.7 magnum.
The check engine light came on after putting gas in it from a station I do not frequent. The truck had similar problems. I put gas in from my regular gas station and the check engine light went off and it now runs great. Could I be paying for water? The gas was 5 cents cheaper. If anyone knows what could be causing this please let me know, I really need my car to be running reliable. Oh, by the way, my car is a 1998 with a 420 AEM intake, pacesetter headers, 2 1/2 in custom exhaust with magnaflow cat and summit racing muffler.

 

[BoostActionBob]

first off for your idiling at a stop light problem. did you check your tps and isc. they could be the culprit. also check the throttle cable. does it give you any problem at all when your driving.

second for the gas thing. the check engine light will come on if there is the wrong type of fuel ran through it and the o2 sensor doesnt like it. a dealership up here put diesel in my tsi and i got 2 new o2 sensors out of the deal. you may of had a bad tank of gas and got some good stuff put in and all the bad stuff burned of your o2.

 

[old man]

Thank you BoostActionBob, I thought it may be the thottle position senser but I don't know much of anything. I don't know what a ISC stands for. I went from 70's and 80's camaro's to this new stuff, gladly. I am a virgin, please be gentle and slow. This is my first time.

 

[Slammed0]

Mine acts wierd too.


If I pull out the clutch while driving the RPMs will only drop around anywhere from 1200-1000 and just sit there until I am completly stopped. Then they will drop down to normal.

And sometimes in stop and go traffic when I push in the clutch the RPMs will jump up 100 or 200 rpms.

 

[BoostActionBob]

like i said your first step should probally check the throttle position sensor and the idle control sensor. and maby even the throttle cable. cleaning your throttle body and intake manifold and mas i had idle surge like you are describing and i did all this and the cleaning fixed it.

 

[AnkurJ0217]

Can an idiling problem and check engine light be a result of an internal breakin like a lifter of something? it will most likely not be anything serious right? if its just a boost leak, ISC, or TPS, then its not major...not much money to spend to fix this problem. Im looking to purchase a 99 eclipse with 93k miles with idiling problem and SES light...the spanish dealer wants to sell for $4900 after bargaining...still have yet to decide. Its a clean car...no accidents nothin like that...its clean. just idle issues