High idle

[freshtiva]

I bought a 1992 gl, five speed, EFI, with air a month ago, The block or head was cracked. I bought a different motor from a FFC member installed it and engine fired right up, no leaks, fluid loss, or cooling problems. It has one little quirk though. With new motor it idles at 1500 rpm. Also I notice that the RPM stays up a little between shifts, doesn't fall off like my other festivas. Occasionally at a stop light the idle will go back and forth from 1500 rpm to 1700 rpm four or five times in a matter of 15 secs then settle back to 1500. The car had working air but because of rusted treads in the engine block I was unable to remount ac bracket. Don't know if this is related or not. I know functioning ac has effect on idle speed but cabin switch for ac hasn't been pushed in when this occurs. One other symptom is that when you back of the gas pedal like you would to maintain speed on a down grade ( just let off slightly ) its like you had taken your foot off the pedal completely. Car never acts like its going to die or anything its just a drivablity thing. When I made engine swap I used the original Throttle body, intake plenum and original injector rail. I did put some injection cleaner in the first fill up but it was idling high prior to that. Car didn't do this with original engine. All hose seem connected properly. Thanks for any help !! I'm searching in shop manual but haven't found solution yet.

[ericsmith32]

Timing?

[freshtiva]

Put new timing belt on and didn't alter distributor position? Runs good through full range, starts easy, never misses, sputters or cuts out, just the high, and occasional sporadic idle. The oxygen sensor is not from original car. Put on new fan switch and temp sender. Anyone ever have a fuel pressure regulator, or throttle position sensor problem that sounds like my symptoms? I am thinking its in the fuel system and/or related signals to or from PCM? (I know that doesn't really narrow it down much) Don't know. Also, does anyone have a "Power train control/ emissions diagnosis manual " my service manual refers to?

[FestYboy]

you do realize that there's an idle adjust screw on the throttle body along with an air bleed screw that can be adjusted...?

just a thought

[ericsmith32]

If he didn't adjust anything he shouldn't have to mess with anything. My aspire does the same thing, different systems but I haven't figured it out yet. The funny thing is mine returns to normal anything over 70 or 80 degrees, the colder it gets the worse.

[freshtiva]

Yeah it idled fine and didn't have other symptoms with original engine. I know about idle adjustment screw, I read the entire fuel charging chapter in the service manual. Some things sound like they might be the problem but I hate to start messing with thing that don't need messed with until Ive got feedback from the experts @ FFC. Appreciate any input you have, I may be off the mark in my diagnosis. To recap symptoms:
1. High idle 1500 RPM
2. Slow RPM drop between shifts
3. Occasional sporadic idle goes back and forth from 1500 to 1700 RPM four of five times in a matter of 15 sec then settles back to 1500 RPM ( The first time I noticed this is was when the cooling fan came on, fan sounds like it may be going bad.
4. Slight let up of gas pedal feels like you took foot completely off gas, but then resumes normally when pedal is slightly depressed again.

[FB71]

sounds like its going lean. Did you check or replace the intake manifold gaskets?

[getnhi1]

Check the intake hose for leaks, and vac leaks, readjusting the idle is a snap on the 97, shouldn't be much different.

My car had a leak in the intake hose so some yahoo just readjusted the idle to compensate, once I sealed up the leak the idle went crazy.

[freshtiva]

sounds like its going lean. Did you check or replace the intake manifold gaskets?

I never separated the plenum from the throttle body but I did initially use the old gasket between the plenum and the block. It leaked a couple of drops of antifreeze from that area so I replaced that gasket ( between plenum and block) and that took care of leak. I'm sure that gasket sealed up tight. But I been thinking that it is running lean also. Ill triple check all vacuum lines and hose but I believe they are good.

[freshtiva]

Check the intake hose for leaks, and vac leaks, readjusting the idle is a snap on the 97, shouldn't be much different.

My car had a leak in the intake hose so some yahoo just readjusted the idle to compensate, once I sealed up the leak the idle went crazy.

Ill check for leaks and bad clamps, don't like those limp clamps you take off with pliers. I am trying to keep from being the Yahoo who tries to adjusts the wrong thing. Guess if I cant figure it out Ill live with it. Hate to do more damage then good.

Maybe its just this ones personality!!

[eye_of_ra93]

Is it FI, some times those vacume leaks can cause irregular idle speeds, my 93 FI 1.3 would idle really high, I would play with it alot, at times trying to get it to pass emissions was a pain when the fan would come on idle would go up. I would say adjust timing and play with the idle screw on the intake throttle body.

[freshtiva]

Up date :

Screwed idle air adjust screw all the way in and Idle RPM drop to about 1200 RPM from 1500. Adjusted screw back out one full turn. Didn't seem to be much of a factor.

[ericsmith32]

Which one did you adjust the one on top or the one on the side. The one on top is the air/fuel ratio adjustment.

[freshtiva]

I adjusted the one on top under the black plug by the throttle position sensor. I think it regulates the amount air going through the bypass when idling. I don't see any other places to adjust other then the throttle stop screw. I'm wondering now if idle air control valve is working, maybe its stuck open

[69shelby]

Check your dashpot, it pushes the throttle pack down, I am having the same issue and checked mine and it was stiff, so I tapped it and worked it a little, it is now a little better. Check you car and see if you can push the butterfly closed with your hand.