Idle problems: high, low and very annoying

SVX8588 · #1 10-16-2014, 08:54 PM

So, my car has had an idle problem that has been getting a lot worse recently. The engine seems to run fine when driving and has normal power.

When I start it cold (any ambient temp), it idles right up to about 1500 rpms. Then when I put it in gear, the rpms drop down because of the load. Then I usually drive it about 3.5 miles to work. On the drive, it will do anything from low bouncing idle to extremely high idle (2200+ rpms) if I shift to neutral.

I have replaced all the coils in the last 8 months, cleaned the idle control valve, cleaned the aux idle control valve, replaced the coolant temperature sensors, replaced all vacuum hoses, cleaned the throttle body, checked to make sure the throttle cables are not binding, cleaned the engine ground, seafoamed.
The only thing that seemed to make any difference at all was the seafoam, and it only helped temporarily.

I have concluded that it is an electrical problem and heres why: I have found that while driving, if I shift to neutral (when it's idling high) and flick the key from on to off and then back on quickly, the idle will immediately drop to a more normal range (700~900 rpms).
Also, if I park somewhere after driving and shut it off and then immediately start it again the idle will frequently be different that just before shutting it off. For example, if I pull in somewhere and it's idling at 900, I'll shut it off and then restart and the idle will be at 2000. Sometimes the opposite happens. It's totally random - I can't find any rhyme or reason to it.

Any and all help would be greatly appreciated!

Chucksta · #2 10-17-2014, 01:19 PM

Random thought here, but one that's easy to check out. Press the "economy" button on the climate control and see what happens. On mine, there is a bout a 200 rpm difference between "auto" ( around 800 rpm ) and "economy" ( about 600 RPM) .. If the random rpm fluctuations only occur on one setting or the other, then it would indicate that the ECU is causing the issue. The off and on with the key sorting it out would seem to me that the problem is electronic in nature.

Long shot, but an easy test..

good luck.

SVX8588 · #3 10-18-2014, 12:53 PM

Thanks for the suggestion, but I've tried all settings on the climate control and nothing makes a difference.

Chucksta · #4 10-18-2014, 03:26 PM

Swing... and a miss..

Well, seafoam helped it, but only temporarily..

Seafoam can send a lot of stuff down the tail pipe. How does it run if you disconnect the o2 sensors?

YUP... I'm reachin here..

92snowmachine · #5 10-19-2014, 08:50 AM

Sounds like a vacuum leak. Have you tried unplugging maf?

SVX8588 · #6 10-19-2014, 04:19 PM

Quote:

Originally Posted by Chucksta

Swing... and a miss..

Well, seafoam helped it, but only temporarily..

Seafoam can send a lot of stuff down the tail pipe. How does it run if you disconnect the o2 sensors?

YUP... I'm reachin here..

I haven't tried disconnecting the O2 sensors. I'll do that once I get the subframe back in

Should I try driving it with them disconnected, or just idling?

Quote:

Originally Posted by 92snowmachine

Sounds like a vacuum leak. Have you tried unplugging maf?

No vac leaks, plus cycling the key wouldn't make a difference if it was. I have tried unplugging the MAF sensor - it kills the engine.

Conn SVX · #7 10-19-2014, 04:21 PM

Disconnect then start the engine.

SVX8588 · #8 10-24-2014, 09:00 PM

I tried disconnecting the MAF sensor and then starting the car and driving. It runs terribly and doesn't seem to help with the high idling.
Then I tried disconnecting the O2 sensors and driving. It seems to run okay, but doesn't help with the high idling.

What other sensors could be telling the ECU that it needs more air? Knock sensors? anything with the EGR? (or is that strictly mechanical?)

Chucksta · #9 10-25-2014, 01:22 PM

Hail Mary, full of grace..

" replaced temperature sensors"..

From what little I know of the temp sensors, one is for the dash gauge, one talks to the ECU.. Bad ECU temp sensor, or, a bad wire to the ECU temp sensor would look the same to the ECU. The ECU temp sensor presents a variable resistance load as it's methodology of function. The FSM can tell you which pin to get a reading from with an ohm meter, and the proper range. A DOA brand new sensor isn't beyond the realm of possibility. The reading should be stable, and change slowly as the engine warms from cold. Wire, alligator clips, electrical tape . you want that mess in your hand to be the bridge from the sensor to the wiring.. be sure that the connections are tight, now you can manipulate the leads heading back to the harness and verify that it is or isn't bad wiring in the harness or connector.

Other stuff to try that will convince the neighbours that you're crazy...

When it's on it's high idle, open and close doors, hood, and trunk. Now do it again, and this time slam them hard. You'll be sending a shock wave of vibration through the entire wiring of the car. Vacuum leaks, on the other hand, wouldn't be affected..

When the idle is high, take a propane torch, open it all the way, but don't light it. Run the nozzle right up along all vacuum lines and listen for even the slightest change in engine note. Don't smoke.

"replaced all vacuum hoses" ALL of them? If it's a leak, it may not be under the hood. When you stop the car, and immediately open the gas cap, do you hear the hiss?. The EVAP system pulls fumes from the tank and does ... well I'm not quite sure what it does.. but the point was that if it was sucking as it should, and there was no hiss, something may be blown and sucking what it's not supposed to. Electrically, I mean. As in it could possibly be a vacuum line that isn't supposed to always be under vacuum. As you noted, cold start and idle is fine.. The EVAP system is the first vacuum system that comes to mind where lines are not always under vacuum. The ISIS valve uses a vacuum to open up, but the vacuum is controlled by something else.. I'm sure there's way more examples. It may be and electrically triggered vacuum leak.

Gas tank vacuum lines are accessed through the hatch located under the rear seat.

Smoke test the vacuum line system. Section at a time, with an eye towards parts of the system that are not always under vacuum. My WRX threw the gas cap code at me. It took smoke to find it wasn't the hoses, it was a crack in the plastic junction piece. Google gave some great links for a DIY smoker.

Now, if your neighbours were watching while you were slamming everything shut, and saw you with the propane torch, start the smoke machine and run towards them yelling "RUN !! she's gonna blow".. make sure you're rolling tape..

Yes, I do have a twisted sense of humour.

The problem is that the problem is intermittent. Those are the hardest to fix. Once every few days, I get a little light on the dash that says "brakes".. Would I like to know why it came on... oh hell yeah! I've read somewhere that brakes are an important safety feature.

Will it stay on until I get home or to the garage... no. ( sigh).. It sucks when a bit is just a bit ill.. Just die, already, so I can find you and fix you..

Good luck..