BlackOp

I'm pulling my intake and replacing all my vacuum lines soon. My car (85.5) runs great except it likes to dip down to about 750 RPMs at stoplights then grumble a bit. It corrects itself but is very annoying. If I run my AC it drops another 400 rpm. I'm not sure this is a sign of a faulty ISV...I've searched but have not found anything conclusive. It doesnt spike and stays consistent once it calibrates. Would replacing the alternator help stabilize the low RPM idle/ ac draw? It does this cold or warm...have new wire/plugs/cap/rotor/injectors.

Thanks

Toran

I'm having a similar issue with my 86, it has a rough low idle but drives just fine.
Car has new wire/plugs/cap/rotor/voltage regulator/vacuum hoses. I have another ISV to replace the current one. At that point should replace the old hoses associated with the ISV. Should anything else be considered while in there?

BlackOP when I replaced the voltage regulator it prevented dips while the ac was running.

choinga

I had all kinds of weird idle problems - but the worst was when I'd clutch at say 2500RPM and go into neutral...the idle would bomb out and sometimes the car would even die. I replaced both my ISV and my TPS with brand new units and haven't had any idle problems since.

It could be your idle screw though too - I've read that folks have had issues with theirs backing out or vacuum leaks in that area that cause idle issues.

BlackOp

I adjusted my idle screw today to just below 1000 and it runs perfect now. Idles @ 950 with the A/C on with no grumbles...perfectly smooth, like a new car.. Hurray....

Toran

I may look into the idle screw adjustment too.

Weird enough but since this rough idle issue I think the car is burning less gas.
Over the years a full tank would allow about 310 miles
With rough idle over the last couple months I get like 350 miles.
I am doing the same kind of driving and refilling when the needle is on E.

Does that make sense to anyone?

BlackOp

I used a 9/32 socket and turned it counter-clockwise about a full turn. I cant believe this was my issue...took all of 30 seconds.

Mighty Shilling

did you do it the Proper way by getting the engine completely up to operating temp, then disabling the ISV and adjusting it then? or did you just f*ck with the idle screw?

BlackOp

No...I was so frustrated I gave it a twist. Car was on and up to temp though. I figured I could always move it back to where it originally was. Worked for me.

Clark's Garage listed American 944's @ around 900 +/- 50. Mine was set too low. I may fiddle with it but the extra 40 isnt really discernible (to me). The shudder at every stop light is gone.

BlackOp

Just wanted to follow up...drove my car about 100 miles today, 1/3 being in bumper-to-bumper traffic. It drove perfect...I no longer hate my car. The end.

Toran

Is this the idle screw?

BlackOp

No, the one to the left is...facing down. It's not really a "screw". Counter-clockwise to increase the idle...

Toran

Auhhh the yellow smiley face than!

BlackOp

That's it...calling it a screw threw me off too.

Toran

Thanks BlackOp!
I get to learn about the car and work on my mad photoshop skills at the same time!

BlackOp

I'm curious if this fixes your issue as well....sounds exactly what mine was doing...report back. I was going to replace my ISV, FPR, FPD, TPS , voltage regulator and vacuum lines. That's how fed up I was.....I have an O2 sensor I have to return now.