LQ1 intermittent high idle

[Galaxie500XL]

My '95 LQ1 is doing some strange stuff...at times, the idle is fine, at other times, the idle is way high, 1500 RPM plus. I've checked for vacuum leaks, none found so far.

 

Otherwise, the car is running beautifully, I'd guess this is an issue about 30% of the time. Any suggestions?

[jeremy]

How does the LIMG look?

[spiderw31]

Throttle plate sticking maybe? Does the problem still happen if the IAC is disconnected?

[Galaxie500XL]

The lower intake gaskets were replaced about 400 miles ago. No water leaks, but it's hard to determine an air leak. The idle quality is the best I've ever had (when it's not high idling).

[RobertISaar]

possibly an intermittently bad TPS.

 

does it always seem to cure itself if you shut it off, then start it back up?

[Galaxie500XL]

Sometimes. I'll drag out my scantool. It will show me the IAC position, and the TPS voltage and % of open. Might find something there.

 

Thanks!

[Galaxie500XL]

It looks as if I may have a flaky MAP sensor...there's a '93 Lumina LQ1 in the local yard...is the MAP sensor the same from '93 to '95?

[RobertISaar]

the 94-95 LQ1 cars don't have MAP sensors.... MAF only.

[Galaxie500XL]

I meant MAF...got 3 hours sleep last night, besides, got used to dealing with MAP sensors when I had the LeBaron...

 

So, are they the same '93 to '95?

[RobertISaar]

the 94-95 LQ1 MAF is the one you want. there are no 93 MAF LQ1s.

[AL]

According to rockauto, a 3100 MAF is the same part number so you can steal one of those

[RobertISaar]

i'd be careful there, i know the 94-95 3100 MAF(only on a-bodies) are a way different size, but the 96-up 3100 may be the same one the 94-95 LQ1 uses.

[AL]

I looked it up for a 99 GP 3100

[RobertISaar]

rockauto also states that the 93-95 3100 W's use a MAF...

 

autozone(awesomely reliable source, right?) does have the same P/N for a 99 3100 and a 95 LQ1 though.

[Galaxie500XL]

You guys give great information! I think I've found the problem, the PCV hard line is cracked, and leaks. I haven't found another one yet, but I did find a '93 Z34 in the local junkyard, the hard line on it ran around and behind the plenum, rather than under the mass of hoses on the driver's side. I'm tempted to just use the '93 hose--it only cost me $2.50, much cheaper than a new one, and has the virtue of allowing me to fix it immediately.

[Galaxie500XL]

Well, replacing the PCV hose took care of the vacuum leak, but idle is still occasionally high, but not as high as it was. That '93 Z34 had the IAC still on the motor, is it the same part as my '95 LQ1? If so, I'm tempted to get it...shouldn't cost more than about $10.00 from the junkyard.

[RobertISaar]

should be the same.

 

according to rockauto, all 91-95 LQ1 IACs are the same.

[Highmilagecutlass]

I wonder if your T.P.S is Malfunctioning ?

Some of the things that I've read about the T.P.S on my engine is that it's none adjustable and that the computer takes whatever voltage reading it has at the T.P.S. and uses that establish the idle..or throttle position.

 

I found some pretty use full videos on You Tube to test that with a Volt meter.

 

I'm not an expert on the subject but I think it's worth checking

[Galaxie500XL]

OK...I got the IAC from the '93 Z34. The pintle on my old one looked like a golf ball. Cleaned the passage, and the "new" IAC with throttle body cleaner. Idle is still intermittenly high, around 1500 RPM. Sometimes, shutting it down and restarting drops the idle, at other times, it does not. Any other ideas?

[Highmilagecutlass]

Have tried disconecting the battery cables for a few minutes and doing a idle relearn ?

I think by disconnecting the battery the computer does a diagnostic check. It's kinda like rebooting your computer when it's giving you grief.

[RobertISaar]

when you pull the cables(or fuses, much simpler), after a few seconds the computer loses all of it's SAM(stay-alive-memory), which forces it to relearn a lot of things, minimum TPS voltage included.

[Galaxie500XL]

I'll give that a try, couldn't hurt anything...

 

It did seem to be idling more consistently this afternoon, maybe it takes awhile for it to unlearn a bad habit.

[jongrappin]

Galaxie, did you fix your idle problem. I am having the same issue.

[Galaxie500XL]

Sorry it took me so long to reply, been on "vacation"...working on cars.

 

It was still doing it as of this morning, but finally got my scantool working again (it's nearly 20 years old)...looks as if the suggestion that it may be the Throttle position sensor was right on. Sometimes, the computer says the throttle is closed (0%), and at other times it shows 3%. When it shows 0%, it idles fine, at 3%, it idles high...makes sense, the computer thinks I'm holding the throttle open!

 

Advance Auto Parts has a replacement for $23.09...I'm not a fan of BWD stuff, but in this case, it's hard to go wrong.

[Galaxie500XL]

Well, the throttle position sensor did the trick. The old one was full of nasty stuff, mostly plastic dust. The sensor appears to have been original to the car. Anyhow, it idles very nicely now! Thanks to all who helped!