Erratic Idle Problem [Archive] - Forum


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12-31-2004, 04:48 PM
Well, I have been trying to troubleshoot this for a while. My warranty ended a couple months ago, and now my vehicle has a problem at idle. It sounds like the engine is trying to compensate (rpms go from 450-650 repeatedly); almost as though the vehicle is going to stall sometimes. All my interior lights and headlights also dim and brighten in reference to the rpms going up and down. No problem when the vehicle is moving though.

I get no trouble codes, and the alternator tests fine. I even cleaned out my MAF with electronics cleaner (no residue type), cleaned the throttle body and the idle air control valve. Checked all the hoses for possible vacuum leaks, still turned up nothing. Plugs and wires are good.

I will be running some diagnostics on the engine management (MAF, IAC, TPS, EGR, etc) using Autotap sometime this weekend, but I have a feeling nothing will turn up.

Any ideas? For right now I refrain from driving the vehicle around. I take my truck when I need to go somewhere. I have an optima red top, and it does read a little low when the engine is off (~12.1, lowest 11.89); even when driving long distances it doesn't fully charge back up to 12.5V. I read approx. 14.5V when the engine is on. Could the battery cause a problem with the idle when the vehicle is running though? If so, no biggie, the battery still has three years on warranty.

I'm deploying in about two weeks, and need to get this fixed before I go. When I get back sometime in May this vehicle is being traded in for a 2005 GTO that I ordered this week.

12-31-2004, 05:08 PM
mine does this as well....any suggestions guys?

12-31-2004, 07:32 PM
I'd take that battery out of the car and get it tested on it's own. If it is bad, your alternator keeps trying to charge it up at idle which can lead to that up and down fluctuation.

01-02-2005, 08:53 AM
Took the battery to Advanced Auto and they tested it; it passed test except for low charge, so it is there getting charged right now. After that I'll put it back in the vehicle and see what happens.

[Later that day...]

Results: Put the battery back in the vehicle (voltage is good at 12.5), still same problem with the idle. Ran Autotap diagnostics, looks like I have a lean fuel condition resulting in a long term fuel trim of 21.9% on bank 1 (23% is the limit where a P0171 DTC is produced). I'm thinking maybe dirty fuel injector(s). Fuel pressure is good, and since only one bank is having the problem, doubt it is the fuel pressure regulator or fuel pump. I have already used some fuel system cleaner a couple weeks ago.

MAF, TPS, IAC, etc tested out fine (voltages and readings within specifications at idle and throttle down).

I have read about people having problems with the Upper and Lower intake manifold gaskets going bad. Can this cause idling problems as well?

I'm almost at that point where I am going to just take it in to the dealer - and wait for them to blame something aftermarket on the vehicle.

01-14-2005, 08:53 AM
not sure about the 02 , bu the 00 has only one O2 sensor before the cat and one after, even though it states bank1, these is no bank 2.

01-14-2005, 11:03 AM
mine does this too, but only in extreme cold it seems.