Weird Idle Problem
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 859
Likes: 8
Weird Idle Problem
Hey guys,
Ever since I've bought my 85 (2 weeks now,) I've had a minor problem with the idle. For a while when I first start it up, the idle is fine, staying at 1100 steady. However, once the car warms up, the idle begins to go up and down slowy, between 600 and 700. It doesn't stay in one place, it just seems to move constantly between 600 and 700. It doesn't go much above or below those numbers. This causes the lights and the dash to flicker slightly. I thought a tune up would solve the problem, but after changing the plugs and pcv valve, the problem remains. I am still going to change the air filter, plug wires, cap, and rotor, though I doubt that would be a solution for the problem. Any ideas?
Ever since I've bought my 85 (2 weeks now,) I've had a minor problem with the idle. For a while when I first start it up, the idle is fine, staying at 1100 steady. However, once the car warms up, the idle begins to go up and down slowy, between 600 and 700. It doesn't stay in one place, it just seems to move constantly between 600 and 700. It doesn't go much above or below those numbers. This causes the lights and the dash to flicker slightly. I thought a tune up would solve the problem, but after changing the plugs and pcv valve, the problem remains. I am still going to change the air filter, plug wires, cap, and rotor, though I doubt that would be a solution for the problem. Any ideas?
Advanced
Joined: Jan 2006
Posts: 60
Likes: 0
From: Ukiah CA
This could have been me writing this post. My 85 is also about two weeks new-to-me and it had the same problem with a rolling idle. Worse though, 400-900 and would sometimes die.
I asked about it here.
The cheapest advise given has helped enormously. Dump a bottle of injector cleaner into a full tank of gas. I used Berrymans. It still idles weird sometimes but nothing I can't live with. Also, I've been using Chevron gasoline with that Techroline stuff.
Good luck
I asked about it here.
The cheapest advise given has helped enormously. Dump a bottle of injector cleaner into a full tank of gas. I used Berrymans. It still idles weird sometimes but nothing I can't live with. Also, I've been using Chevron gasoline with that Techroline stuff.
Good luck
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 859
Likes: 8
Thanks for the advice guys. I will try buying a fuel additive and see what happens.
As for the Seafoam, I actually bought a can and tried it out last week. I poured it in very slowly through the pcv valve. I used about 1/3 of the can. I was really disappointed though, because you're supposed to see a lot of smoke come out the back, and I saw none at all. Even after I let it sit for 15 minutes, it seemed to have no effect. Maybe I poured it too slow or didn't pour enough. I'll probably try adding the rest of the bottle this week and see what happens.
As for the Seafoam, I actually bought a can and tried it out last week. I poured it in very slowly through the pcv valve. I used about 1/3 of the can. I was really disappointed though, because you're supposed to see a lot of smoke come out the back, and I saw none at all. Even after I let it sit for 15 minutes, it seemed to have no effect. Maybe I poured it too slow or didn't pour enough. I'll probably try adding the rest of the bottle this week and see what happens.
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
You poured it through the PCV valve? I was told it was supposed to go through a vacuum line and you're supposed to use the whole can. But if its not smoking then maybe it just didnt need to be cleaned. Have you inspected your heads for carbon?
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 859
Likes: 8
No, I haven't inspected my heads for carbon. However, I think there should at least be some smoke coming out, just from the Seafoam burning. I'm pretty sure that pouring through the pcv is the correct way. I'm not sure if more is needed or what.
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Melting Slicks
Joined: May 2004
Posts: 2,524
Likes: 10
From: Lufkin Texas
St. Jude Donor '05-'06
Go to forum member 65Z01's site for info on servicing the IAC (idle air controll) and many other helpful c4 tips. Might fix the trouble.
http://www.geocities.com/jgkov/index.html
http://www.geocities.com/jgkov/index.html
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
This stuff worked great for me
http://www.bgprod.com/
If sounds like the engine is doing a slight hunting,I would check for vaccum lines for leaks and see if the gas cap is on tight for starters.
http://www.bgprod.com/
If sounds like the engine is doing a slight hunting,I would check for vaccum lines for leaks and see if the gas cap is on tight for starters.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Posts 9 and 10 is what I would be looking at, common problems. Hunting for idle sounds more like IAC adjustment. Pouring a can of something in it isn't a fix, use the search feature above you will find many posts/threads reagrding "hunting" for idle etc.
Last edited by mseven; Feb 13, 2006 at 06:36 AM.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Hi. I have an 85 4+3. Have had the same idle problem..The first thing you should do is to check the TPS voltage. It shall be between .54V to .64V and then to clean the throttlebody from carbon deposites both at the butterfies and in the IACsystem. The IAC valve is also one main cause of bad idle. If this do not help you should search for vacuum leakage. Check all the vacuum hoses also underneath the pleanum. If they are ok chek for leakage at the runners. Spray either propane or start gas around the runners systematically. If the idle rpm changes it is a leakage. I had that. And changed the gaskets and ensured that the surfaces were in good condition . I also had silicon between the gaskets and the surfaces to ensure that there should be no air coming through. After this do a minimum idle air adjustment to ensure that this is all right. If it is to low the ECM tries to corrct it and you may have a cycling idle.
I had in addition a bad EGR valve so I chnaged that. Now the idle is good.
Good luck
I had in addition a bad EGR valve so I chnaged that. Now the idle is good.
Good luck
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
I dis-agree, setting the TPS should be just about the last thing you should do when setting minimum air(idle). This is because when setting the the min. air at the throttle body, the TPS voltage can change.
Taking the IAC out of the picture is first thing to obtain minimum air /idle, then following all the rest of the procedures. Do a search on minimum idle or setting minimum air, or read your manual, there is a whole page dedcated to setting minimum air/throttle body adjustments.
Taking the IAC out of the picture is first thing to obtain minimum air /idle, then following all the rest of the procedures. Do a search on minimum idle or setting minimum air, or read your manual, there is a whole page dedcated to setting minimum air/throttle body adjustments.
Last edited by mseven; Feb 13, 2006 at 09:04 AM.
Melting Slicks
Joined: Aug 2003
Posts: 3,377
Likes: 387
From: Lakeville MI
Your idle sounds perfectly normal to me.
The idle rpm is only controlled to +/- 50 rpm anyway, under ideal circumstances, and with the low resolution digital dash, the display is going to tend to jump up and down around the control point.
If your lights dim or flicker, your alternator may not be keeping up at the low rpm. This is common with pulley kits.
The idle rpm is only controlled to +/- 50 rpm anyway, under ideal circumstances, and with the low resolution digital dash, the display is going to tend to jump up and down around the control point.
If your lights dim or flicker, your alternator may not be keeping up at the low rpm. This is common with pulley kits.
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 859
Likes: 8
Originally Posted by tequilaboy
Your idle sounds perfectly normal to me.
The idle rpm is only controlled to +/- 50 rpm anyway, under ideal circumstances, and with the low resolution digital dash, the display is going to tend to jump up and down around the control point.
If your lights dim or flicker, your alternator may not be keeping up at the low rpm. This is common with pulley kits.
The idle rpm is only controlled to +/- 50 rpm anyway, under ideal circumstances, and with the low resolution digital dash, the display is going to tend to jump up and down around the control point.
If your lights dim or flicker, your alternator may not be keeping up at the low rpm. This is common with pulley kits.
Racer
Joined: Feb 2000
Posts: 372
Likes: 1
From: Victoria British Columbia
Originally Posted by C4driver99
mine idles 600-700. I thought it was normal. Maybe your just not used to it because most other cars are not digitally displayed. 
Drifting
Joined: Apr 1999
Posts: 1,261
Likes: 6
From: Middletown New Jersey
Originally Posted by gregm999
Yeah, I do suspect that the alternator is going. The voltage tends to jump up and down between 15 and 12 volts, and when I put my foot on the gas, it has no effect on voltage. Sometimes voltage will even dip low enough for the voltage light to go on.
