Rough idle

[rrhartjr]

I have a 92 NA wagon that idles roughly. It bounces around from 400 to 700 rpm when stopped.

Any suggestions on things I can test to try and figure out what the cause of the problem is?

[Legacy777]

Can you provide any further information about the car or the problem? When did it start happening, does it do it all the time, or just when cold or hot, etc, etc.

[rrhartjr]

It only seems to do it after warming up, and sometimes it will warm up and idle fine. Probably 2 of 3 times warmed up, it idles roughly. I've owned the car for 9 months, and it always did it to some degree. But it seems to have worsened recently to the point where it bothers me enough to do something about it

It drives just fine, the engine seems to run strong. I recently replaced the timing belt, and it idled funny before and after.

Nothing special about the car, its a 92 NA wagon, 2.2L engine, 2WD. No hubcaps.

[Legacy777]

Have you done a tune up on it, changed plugs wires, fuel filter, PCV valve, etc?

How many miles are on it? Do you have any service records from the previous owner?

Does it do it only initially after warming up, or does it continue to act funny even after driving it for a while?

[rrhartjr]

I've done plugs and wires since I've owned it.

278k miles.

If it idles rough after warming up, it will act funny at idle until the engine cools down again. And then you get to roll the dice again to see if it will act up.

[Legacy777]

Hmm....it could be a slew of possible things. Some cheap things to try is running some seafoam through the PCV valve to help clean things.

Another relatively cheap thing to do is replace the coolant temp sensor, since the ECU can behaive kind of funkily if it's not working correctly, and with the mileage on the car....who knows when it was replaced.

Maybe someone else will chime in with some suggestions.

[rrhartjr]

If the dash gauge for engine temp reads normally, does that indicate a healthy coolant temp sensor?

[Legacy777]

No, the dash gauge temperature sensor and the ECU temp sensor are separate. Plus, even with the sensor appearing to read correctly, it could still have issues. It's hard to explain, but I've experienced it, as well as others on the board where the sensor may have been slow to react, and caused some weird issues.

It's only like $20, so it's not an expensive investment.

[tahiti350]

Mine does the same thing, but I know the TPS and base throttle setting need to be re-indexed (I was messing with them before I found that my IAC was toasted).

It could also be the IAC valve, they can develop a "dead spot" that it may have to over comensate for causing the surging.

[Boostedballs]

Mine does the same thing, but I know the TPS and base throttle setting need to be re-indexed (I was messing with them before I found that my IAC was toasted).

It could also be the IAC valve, they can develop a "dead spot" that it may have to over comensate for causing the surging.

I agree with this.
My second thought would be (at that milage) CLOGGED FUEL INJECTORS.

Run some Lucas Oil in the tank from 1/4 tank to almost empty. I wouldn't bother filling up past half a tank to keep the concentration high. I noticed a real difference with my 93 N/A after this. I would buy 2 of the large bottles of Lucas Oil ($10 ea) and that should get you through about 10 half-tanks.

Seafoam works also but more expensive. When I change my fuel filter, I always fill the filter with straight Seafoam and only let the engine run for 20 seconds or so. Then I shut it down and let the Seafoam soak into the fuel injectors for a few hours before starting the engine again.

might want to change your plugs after this treatment.