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Grand Marq won't idle....

5K views 12 replies 4 participants last post by  shotgunsmitty 
#1 ·
Hi, I know I should introduce myself in another forum, but my name is Skip, I live in Austin, Texas.

I have an older Grand Marquis, it's a 1988 with the 5 Liter V8.
It's a nice running car, big ol' boat that I love to cruise around in, but I have a problem that I hope someone could help me with.

She won't idle. She'll start, and will run with your foot on the gas, but for some reason, and I'm not sure why, she just doesn't idle. I'm hoping that it might be something in the throttle body that's clogged, and I've got some seafoam that I plan on letting it suck up through a vacuum hose to see if that cleans out some stuff, but if anyone has any suggestions, feel free to throw them my way. I vaguely remember an issue that's somewhat similar to this, so if anyone has any info, I'd love to hear it!
 
#2 ·
Do a search for Idle Air Control (IAC) valve on this forum and you might find some useful info. A clogged IAC can cause the problem you describe. A failing TFI (ingnition module) or Throttle Position Sensor (TPS) and also cause erratic idle.

Does it do it all the time or just when the car is cold?
 
#7 ·
IAC worked! It was pretty grungy, brown on all the parts. I removed the electrical solenoid, too, was careful with the gasket, and cleaned everything with lacquer thinner and brake cleaner. After reassembly, it started right up and idles fine!

Very nice call, folks!

Next round's on me!
 
#10 ·
Where is the IAC located? I can't find it on my 94 Grand Marquis.
The car starts up but wont idle at all. Only if I give it gas. I looked around my throttlebody but can't find anything that looks like an IAC valve. There was an electrical plastic part which I took off but that wasn't it. I think that was the TBS sensor which I may have damaged and that's why the thing doesn't start? I don't know... Please HELP...
 
#11 ·
Mine was on the back side of the throttle body, but then again, mine is an 88 with a distributor, no electronic ignition, so yours is probably different. Up from the air box about a foot or so is where I found mine right behind the EGR valve, right in front of the butterfly to the throttle body.

Hope this helps, let me know if it doesn't, and I'll try to take a picture.
 
#12 ·
Hey shotgunsmitty,
Thanks for your help. I did finally find it. It was way low in the very rear of the manifold by the firewall. It is in such a hidden location that I didn't see it right away. It also is in an almost unreachable location. It took me 3 hours, bruised knuckles and a lot of cuss words but I finally swapped it out.
Once I had it removed I noticed the real problem. There was a large hose underneath the IAC that popped off. That hose is even more impossible to reach and I barely got it back on there. I wanted to put a clamp on it but there was no way for me to reach it. I think the only way to do that is to take the entire manifold off and I am not doing that just to put a clamp on a hose. Anyway, I got the hose back on and the IAC replaced and the car runs like a champ now. No more rough idle, it just purrs like a kitten.

Thanks again for your reply.
Have a Happy New Year
 
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