91 Escort GT surges at stop

[lougheed]

I recently replaced my head gasket on my 1.8l (240k miles) and it is running great, except when I come to a stop the engine slowly (30 or so seconds) runs up to 1500 RPM holds for about a minute and then comes down to idle. I just know it is some sensor I hooked up wrong, but I can't find it through trial and error.

Any help would be appreciated.

[mightymoose_22]

I would guess at the Idle Air Control (IAC)... not sure where it is on a 1.8, but best guess is right on top of the intake manifold where the big rubber hose connects.

[lougheed]

Thanks, that made sense to me, so I disconnected the wire harness from it and had the same symptoms. It is so repeatable in time duration, it just seems to me the computer is sending the signal to control this surge and duration. Only other clue, is before the engine warms up, it is fine.

[mightymoose_22]

Dunno what sense you made of it, but I would think if you disconnected the IAC and had the same symptoms then the IAC is likely the culprit.
Do more troubleshooting on the vacuum system to see what you can find out. It might help to remove the IAC and attempt to clean it up a bit and try again.

[zzyzzx2]

How many miles are on the IAC?
I replaced mine at 150K miles, and after I did, I wish I had replaced it earlier.

[lougheed]

It made sense to methat if it wasn't connected it would not be able to receive the signal to open/close airways. It is also idling high at about 1000rpm even after I adjusted the idle all the way down.

[Davescort97]

I disconnected mine and the engine quit and it's working fine.

[mightymoose_22]

I bet the IAC needs to be cleaned... lots of gook can get in there...

Just about every time I have dealt with a "surging" problem, it has been the IAC.

[lougheed]

You disconnect the harness from the IAC and the engine worked fine or it died? Does anyone know the the bypass air should be applied and when it should not?

[Davescort97]

You've got the ISC (idle speed control valve) on the 1.8. The 1.9 and 2.0 have the IAC(idle air control) It does the same thing. You can check it by puttting an ohm meter between the 2 electrical connectons on the valve. It should read 6 to 14 ohms resistance. I can't make any predictions about your system because it is different from what I have. My mistake. Check all the vacuum hoses around the throttle body. Sometimes they get cracked and affect the idle.