97 escort idle problem

[calla1231]

when I go to change gears the idle goes high momentarily. it only does it when changing gears. I can correct it by turning the car off and restarting it. I tested the IAC, thought that was the prob, changed it. after 2 days it started again. I thought vaccum leak but it doesn't do it all the time. all hoses and wires look good. no codes are coming up. any ideas?

[mightymoose_22]

Have you tested for a vacuum leak?

How does the car act at idle while in neutral?

How does it act in neutral at 1500 rpm? What happens when you let off the gas from 1500 rpm?

[calla1231]

I have not tested for a vaccum leak, it's fine while in neutral. I would have to figure out the rpm's, I have no gauge on the dashboard. and it doesn't do it regularly. I drove it to the part store today for brakes for my truck and it was fine, was gone maybe 45 mins. came home and wife drove it to grocery store, 10 min trip, started doing it 1/4 mile from the grocery store. it was fine when she came home.

[mightymoose_22]

My best guess at this point is that it is sucking in air from somewhere.
I would usually suspect the IAC first, but it seems you covered that.

You don't need a tach to measure the 1500 rpm... I just wanted you to rev the engine up to a normal driving range, hold it for a minute, then let off as if you are shifting. You might be able to duplicate the problem.

Get yourself a length of hose to help you listen for possible air leaks at the intake manifold. You said you checked all hoses... make sure you got a good look at the elbow on top of the manifold... it likes to crack on the back side.

[calla1231]

I checked it, it was good. if it was a vaccum leak wouldn't it do it all the time? and like I said if I turn the car off then back on it will stop and be fine for awhile. maybe it's the TPS? my wife says when she drives down the highway it feels as if it's surging and if the speed had increased some even though she didn't give it any gas (she just remembered this). the TPS and IAC were both replaced in Nov. I'm going to check the plugs later just to make sure I covered my bases but I'm stumped. even though it wasn't throwing a code, should I have disconnected the battery for a few after I replaced the IAC?

[mightymoose_22]

No, vacuum leaks are not always constant.
Sometimes they only occur at certain temperatures when parts have warmed up and expanded a bit.
TPS makes sense... especially if you had it replaced with a substandard part.

[Davescort97]

It could be a sticky throttle cable or a dirty butterfly flap in the throttle body itself. With the car stopped and the engine idling in neutral give the throttle a short tap. Get a helper to do this while you look at the throttle linkage under the hood. Does it snap back in place when the pedal is released? You may be able to clean the throttle body without removing it. Get some sensor safe throttlle body cleaner and spray the linkage, cable and throttle flap while moving the throttle open and shut. Do this until everything works smoothly.

[Intuit]

Is it possible that the system is either not recognizing airflow correctly, or is going in and out of warm-up mode ? Try cleaning MAF+ACT/IAT with air filter. If there is a way to check and test ECT, might try that.

Ordinarily you'd smell coolant if the heater core were leaking onto the computer underneath the dash. TPS is a possibility but would find a way to test that prior to replacing. Should be a rare failure item on these Fords.

My IAC is slow to open up which means low idle on cold start until I get moving; then I get high idle, sometimes erratic or unresponsive for the first ten minutes of driving... UNLESS, I shut it off and then turn it back on. Then it behaves as normal. Instead of replacing the IAC, I've simply cleaned and lubed it in the past. I'll eventually get around to doing that again... still original equipment with >240k on it...