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Dan, Technician
Category: Saturn
Satisfied Customers: 23981
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Idle issue - not the IAC or TPS

Customer Question

Idle issue - not the IAC or TPS
Submitted: 1 year ago.
Category: Saturn
Expert:  Dan replied 1 year ago.

Hello, my name is***** the check engine light on? What does idle fluctuate between? Thanks.

Customer: replied 1 year ago.
No check engine light (unless I unplugged the TPS). It will go up to as high as 3000. It seam to idle fine at low temp. Once up to temp it will still will sit at 850-900 or 1800-2000, surging on occasion to 3000 or back to normal idle.
I thought that I had it when it was sitting at 1800-2000 and I unplugged the TPS and it took it down to a rough idle (650 - 850) last night. However, this morning I drove to work (20km/ 12.5miles) and parked. The RPM was 1900 and I though "okay unplug the TPS and it will drop proving that it is the problem." Only there was no change in RPM.
Expert:  Dan replied 1 year ago.

I agree the coolant temp sensor is the most likely cause and I'd replace it. If IAC is sticking unplugging it wont help, you will need to remove iac to manually block off port to see if idle drops. But if iac fails it will usually set codes, the coolant temp sensor wont. Let me know how it goes or if you have more questions. Thanks.

Customer: replied 1 year ago.
I replaced the IAC first thinking that was he issue. I even have the TPS part (have not unwrapped it yet).Now, at lunch I took it for a drive, got it up to temp, and parked letting it idle (800-900 RPM) for 2-3 minutes. Then I brought the RPM up to 2500 for a moment, the engine dropped to 2000. I again unplugged the TPS and this time the RPS dropped.So why would have this worked last night and this afternoon but not this morning?
Customer: replied 1 year ago.
What if I was to unplug the coolant temp sensor. Would there be a reaction that would indicate that this problem?
Expert:  Dan replied 1 year ago.

No, there is no way to test coolant temp sensor without a scan tool. The throttle position sensor would also usually set a code. You can also monitor the signal wire on tps during problem to see if its higher then you know the tps is problem. Let me know how it goes or if you run into more questions. Thanks.