mazdaverx7

On my 86 4+3, I'm battling a high idle condition when coming to a stop. When I press the clutch in while coming to a stop, the engine idle climbs as high as 1800 rpm and I have to blip the throttle to get it to return to 700. Sometimes I have to blip the throttle more than once. It also feels like the cruise control is on when I let off the throttle. The car will stay at a steady speed which is a little unsettling and I find myself braking to slow down wheres under normal driving conditions, letting off the throttle would slow the car down. I removed and cleaned the throttle body and cleaned the IACV and cleaned its seat. I put it back together and checked for throttle cable binding and there was none. I drove the car and for the first 15 miles it was perfect. Then it slowly degraded back to how it was. Figured that the IACV was sticking. And perhaps it still is. So last night I adjusted the TPS to the proper 0.54V and it seemed a little better but still not perfect. Then I attempted to set the base idle by jumping pins A and B in the ALDL connector then removing the jumper, disconnecting the IACV and starting the engine. What I read was to set the base idle to 450 rpm in neutral and then reconnect the IACV. When I disconnected the IACV, the idle shot up to 1800 and lingered there. I plugged the IACV back in and the idle went down to 600 rpm and I adjusted it to 700 rm and drove the car. It drove fine other than the lingering idle. Seemed slightly better as the idle would linger at 1200 rpm and one small throttle blip would take it down to 700 rpm. Looking for suggestions as to where to go here. Maybe replace the IACV?

Dt86

Check your throttle cable to see if it's hanging up near the fully closed position.

FelixP

My throttle does this sometimes, although not as bad. Take the intake boot off and spray WD40 on the butterflies and the shaft, that stops it happening for a few weeks for me.

81c3

Could maybe indicate the butterfly shaft bushings are wearing out.

mazdaverx7

The throttle cable is not binding. There were no vacuum leaks at the throttle body but I suppose that the throttle body could still be faulty with worn throttle shafts. I'll see about picking up another throttle body and giving it a try. I'm also considering ordering a new idle air control valve an installing it and seeing if it makes any difference.

aklim

Crazy idea but ever tried getting readings with a scanner to see what the ECM is seeing?

Cjunkie

Just throwing this out there. MAF clocked in the right position/have you cleaned it since you got your car?

mazdaverx7

The MAF is clocked properly and I did replace it with a new unit. Same symptoms before and after. Thought I believe its gotten progressively worse.

mazdaverx7

Yes, but my Snap On scanner does not have an ALDL adapter. Reading live data would definitely help a lot! I'll see if I'm able to locate an adapter. I borrowed an Autel scan tool from a buddy at work and it had the ALDL adapter but it woudn't go back to 86. It was having a tough time even connecting to the car.

hcbph

Does it ever run 'really rough' as in barely run after a few blocks on a cold day? I had some high idle issues with mine then that started on a random pattern and had a hard time tracking it down. IIRC I was get a code at times (36 or 42 but can't remember which for sure) but even that wasn't consistent, sometimes it happened without any codes.

One day it happened and I had kept coming back to the IAC as a possibility and happened to have a plastic faced hammer with me. I gave the IAC a couple of light raps with that hammer and it smoothed right out. I don't think it's happened again but I keep that hammer in the car just in case. Now when I pull up to a stop light, the idle will drop to about 700 rpms once I come to a full top, where before it usually sat at 1100 - 1500 or better most of the time.

Good luck.

aklim

If that was the case, why keep the hammer around and not replace the item?

Cjunkie

May just be time to get a new IAC

whalepirot

Sure sounds like a mechanical restriction of movement. A bit of lube is way cheaper than e-parts. U probably know K.I.S.S

mazdaverx7

I'll get a new idle air control valve on order and replace it. I don't think it could hurt to put one in anyways and they're cheap enough that if it doesn't fix the issue at least I can rule it out as being a variable and I will know that I have one more newer part on my car.

mazdaverx7

I considered that and no matter how much I mess with the throttle cable and throttle body with the car off or idling, the throttle body always closes properly and returns to the stopper. The idle gradually started doing this within the last 500 miles. Its quite annoying to be honest and I'm going to track the issue down and fix it, lol.

hcbph

Go one sitting on the shelf right now waiting to go in. As long as it's running fine for now, that's a winter project. I'd rather enjoy the car during the short driving season we have here.
Kind of like the interior light delay relay. Needs to be replaced but again that's a winter project.

That's the kind of stuff I save up for when you can't take it out, do it during down time. If it doesn't prevent driving it, it waits till winter typically. Plus I finished off some of those 'must do' projects on the T-Bird recently. They were some that prevented me from driving it, so that took precedence.

aklim

I don't recall stock but replacement is a 5 minute project for a mechanic. OTOH, I would take the TB out and clean it so probably a couple hours if you want to do the coolant bypass for an easier way to get at the TB in future.

mazdaverx7

Ordered the Idle Air Control Valve yesterday and I'm going to install that and see if it helps. I'd rather have a new part in there just to make sure its working properly and if it doesn't fix the issue at least I can rule it out as a possible suspect.

hcbph

I'd love to know how to get it replaced in 5 minutes. I've looked at it and short of taking the TB off, I don't see how you're going to get the iac off any other way.

aklim

Can you take the plug off and then unscrew it? I forgot how to do it already since it has been eons since I had a stock setup but I believe that is how I did it on mine which is not stock. I have a HSR. Worst case scenario is to undo the bolts holding the TB and undo the cables to move the TB slightly and get a socket on it.