jstand22

I have an 87S and the idle has just gotten to be terrible. When first started it barely wants to run, kicks around a little, then even after its warmed up the rpms keep going back and fourth between 800-950ish. However, once over 3k rpms power is awesome, its just the idle is horrible. I just did a full tune up and it didnt go away. Any suggestions on what to check?

Spidey944

high idle is normaly a vacuum leak. the Idle control motor is trying to make up for it, hence, the fluctuation. So it could be a vacuum leak. Find a shop with a smoke machine to test the intake/vacuum system. May even find a few things you didn't know were leaking.

75ohm

Idle motor... probably.

75ohm

As in, idle air stabilizer motor...

GodSpeed

I also think is probibly a vacume leak/s and maybe the ISV.

Keithr726

Like this?

jstand22

haha no its not as bad as that video, keithr, it stays below 1,000 it just goes from 8-950 and doesn't sit solid like it used to.

Luis de Prat

When this recently happened to my 951 it was, indeed, the ISV.

Perhaps yours is leaking? Take some tubing, put one end to an ear and poke the other around under the intake manifold with the engine on to see if you can hear a leak.

harrisonrick

Mine did that just after I put on a hi flow cat...I figure the increased "outgoing" exhaust pulled a piece of gunk into the ISV. On the intake, there's an "access port" I'll call it. I unsrewed it and poured some throttle body/intake cleaner in it, let it sit and drove it.

She'll SMOKE for a minute after you restart. DO NOT pour the cleaner in while running unless someone is is the car and can shut the ignition off as the idle will shoot way up with the "access port" off. Some cars may have some emissions junk there, instead of a cap on the "port", but I think most have it deleted. If that's the case, you'll have to be creative and try to get some cleaner into the ISV by undoing one of the rubber lines. (good luck)

BTW...the ISV is UNDER the intake. A real bitch to get at.

Otherwise if this doesn't work, you likely have a vacuum leak of some sort.

jstand22

Thanks guys, I'll be doing alot of work this weekend (fixing exhaust leak, new rear shocks and sway bar, painting the cam cover) I'll check the hoses and that ISV.

gtroth

When my TPS wasn't actuating, my idle bounced around quite a bit.

That said, I would still probably look into the ISV first. Question - when comming off of throttle, does the RPM drop perilously low, then bounce up? That, I believe, is a slow responding ISV (new ISV fixed that for me).

And of course, as said, vacuum leaks have to be considered when this kind of thing is happening.

jstand22

yes when i let go of the throttle, it will drop rapidly and very low like its about to stall

darren1031

Dont overlook the obvious and the easiest. Check your AFM.
Remove the air filter box and use a screwdriver to see if
the door swings open and close smoothly.

My AFM door was sticking (and even squeaking), causing idle problems.
It's still that way. I have to send it off to get rebuilt...again.

Darren
'87 944S