High Idle

[robertc1024]

I got my '88 Ranger (manual tranny) a few months ago - it had been garaged for basically the previous 2 years. After fluid changes etc. it idled at about 1300-1500 rpm. Cleaned IAC valve, throttle body, linkages, lubed throttle cable etc. and it idled perfectly at ~850 rpm for well over a month. I started it up a couple of days ago and it threw the CEL on and died. Re-started, CEL went back off - after driving it around (ran perfectly) and getting it warmed up, the idle is about ~1300-1400 rpm and it's been that way ever since. Any ideas what to try?

The first thing that came to my mind was if the coolant temp sensor went out and the truck thinks it's not warmed up, wouldn't it also be running rich? It doesn't seem to be, but I haven't pulled the plugs to look at them.

 

[RDR]

just trun the screw on the throttle cable, that connects to your manifold.

 

[robertc1024]

I thought I'd read that the computer controls the idle and that adjustment screw was for something else. Anybody know?

 

[robertc1024]

AAAAARGH - It's getting worse. I backed off the stop screw and it dropped the idle a little. Then drove it around quite a bit hauling stuff. I noticed when I pushed the clutch in it would idle up to ~2k rpm. Stopped at the hardware store - came back out and it wouldn't start. Finally got it started and besides the high idle, ran perfectly. Got home - stopped it again and again, no start. This smells like some kind of computer/electrical thing to me. Ideas??

 

[RDR]

try gettin the codes

 

[RustedRanger]

That screw is to adjust the Throttle Position Sensor (TPS).....now it has to be reset. I did the same thing when I got mine. You can do a search of the archives to find out how to do it. I changed so many parts trying to get mine to idle right that I don't know what was causing the high idle. Your right though....the computer controls the idle using the IAC valve.

 

[robertc1024]

Ok - I've just not had time to get codes - will do in the next couple of days. Rusty - do you know if there's any way to test the IAC solenoid? The working part is clean as a whistle - pulled it off again today and re carb-cleaned it for the second time. I'm starting to sound like the Einstein quote about insanity is expecting different outcomes with the same actions.

 

[RustedRanger]

You can check to see if the IAC is working by unplugging it while its running,if the idles falls down or it dies then it's working........how well it's working is another thing. I did that and mine would die,I cleaned it out and also cleaned the ports(holes) where it mounts and fouled out my spark plugs. My idle got worse even after changing the plugs and while sitting at a stoplight it would die most of the time unless I gave it gas. I tried tapping it with a screwdriver handle with it running and it would die,so I changed it. It was over $70 at Advance,if you do decide to get a new one I'd check at rockauto.com,I got a fuel pressure regulator there and it was $25,at the local parts stores it was around $80! Do you "blank out" the computer after you work on it? Once I put Restore in the oil and Lucas treatment in the gas and it started running worse until I unhooked the battery to clear out the computer,it cant adjust to running better only worse(like as the tuneup wears out).

 

[robertc1024]

Good advice - I'll check it here in a little bit.

 

[robertc1024]

Ok - I got the truck warmed up and while letting it idle, I unplugged the IAC - engine died immediately. I tried the "whack it with a screwdriver test" and the idle didn't change at all. Tried pulling codes and got nothing - BUT - that raised another question. When I turn the key to the run position, the only indicator lamps that are coming on are the two top ones - seat belt and parking brake. I know that sometimes in the past, the two bottom ones - CEL on the rightt - not sure what's on the left - have come on. Before I rip the dash apart to make sure the bulbs are ok, is there some sensor or something that I can unplug and defiantely make the CEL come on?

I've got the battery unplugged right now. Any idea how long to leave it out before the computer re-sets? On my Maxima, it's like hours.

 

[creepinjeepster]

Mines a 3.0 not a 2.9, but I've been having similar issues. I unplugged my IAC and it didn't do nothing but keep running. Guess that's suppose to mean mines bad?

 

[robertc1024]

Or you just might need to clean it - mine idled way way better after I did that. Just pull it apart and clean with throttle body cleaner. Inside, it looks like two balls that cover two ports - I suspect that the computer controls it to let air into your intake since the throttle plate is pretty much closed.

 

[RustedRanger]

I've always heard at least 15 minutes to clear out the computer. One thing my friend who does diagnostics told me to do to help issues with the idle is to soak a rag with carb/intake cleaner and wipe off the backside of the throttle blade. I had already spayed out my intake but I gave it a try and I was amazed at the amount of junk that was on the thing. There must have been at least a 16th of an inch of black crud on the back side of the blade. I don't know that it helped because I had several other problems as well.

 

[robertc1024]

I did that just the other day but I had cleaned it a month earlier and it was still pretty darn clean. Can you offer any help about the warning lights I described above?