Hello all, and thanks in advance.

My most recent journey on my 1986, 5-speed 2.9 idle issue. My issue today: Great idle at cold, and no problem at freeway speed. My issue is that when the truck warms up, she will go to a very low idle, seems to be about 500 RPM or thereabouts, (just by ear haven't put a tach on) and she can stall out. Not ALL the time, just frequently. I'm looking at the IAC.

Today I tested the voltage at the red wire going to the IAC. It had charging voltage, which is good. Ground didn't test as high, but it was way over 12v. I've pulled the connector off while the truck is running, no difference. So, I either have a bad IAC or a vacuum leak, right? Haven't gone the vacuum route yet, but I just went out there and pulled off the IAC. Took off the positive cable and put the key to "run." Went back under the hood and put the cable back on. No movement on the IAC pentil. Now, the truck wasn't down to full cold. As this IAC has 8K on it, I'm not sure if I should... clean it again, or replace it or, let the truck cool down some more. Any suggestions????


Thanks so much,

Tony

More info below:

On this rebuilt engine, I've there are many new sensors and electronics: O2, TPS, IAC, EGR, EEC, ignition module, distributor, cap, rotor wires. I've put on a used EGR relay a few weeks ago as well as a new fuel filter. Oh, btw, new high pressure fuel pump and fuel pressure regulator. None of these items are over 8K old.

 

Red wire on IAC Valve gets battery voltage with key on, same red wire goes to fuel injectors, solenoids, MAF heater, and computer, they all get this 12v from EEC relay
The computer controls the Ground on the other IAC valve wire to open and close the valve.

Remove IAC Valve and plug it in to its 2 wire connector

Turn Key on, engine off
Computer will always open IAC Valve all the way for start up

Look at the valve inside and unplug the 2 wire connector, valve should close, only moves 3/8" but should move
Plug wires back in and it should open
Repeat until you are convinced "it works" or "it doesn't work"

 

Thanks for that, Ron. No movement. Another crappy part, so back to Amazon I go. Unbelievable how these parts don't last.

thanks,

tony

 

Update:

Got the new IAC. Installed it and put it on. Seemed to improve the idle for about half a day. Didn't last. By the end of the day, I'm stalling at lights. The temp gauge is above the first mark, so it's definitely operating temperature. Truck seems to run better below that line.

Didn't have time to do a lot of tests, was hoping that I'd get lucky. The Amazon IAC was cheap enough, and I've got parts to last me till judgement day, so no big deal. Reading through the Greg's vacuum tech article. I have a Mite-e-vac, and will work it. Any suggestions would be helpful. This is pretty frustrating.

tony

 

The computer should bump up the idle if engine starts to stall, IAC Valve is not a "fixed" setting, computer varies the voltage to IAC Valve to maintain "target" RPMs
On cold starts idle will be higher based on coolant temp, usually 1,100 or so
Then as coolant/engine warms up computer will start to close IAC Valve bit by bit to lower RPMs, still based on temperature of coolant

After 5-8 minutes engine should be at operating temp so computer would set target idle of 650 manual trans, 750 automatic

On the throttle linkage there is an anti-diesel screw, looks like an idle screw, its not
This is not your problem but may help prevent the stalling

After engine is warmed up and idling at 650, manual trans
Locate this screw
Turn it clockwise, until idle goes up a bit, then turn it back so idle is at what it was, say 650

Now unplug the 2 wires on the IAC Valve, idle shouldn't change too much, if it drops too much turn screw clockwise a bit more.
Plug IAC Valve back in a go for a test drive

 

 

Hello, and thanks again, Ron.

I've done that, (what I presume is a TPS reset?). Haven't done the test drive yet. Truck was a needle above the first mark on the temp gauge. The temp wasn't changing, so I cranked that screw up, backed it down, and removed the IAC connector. Will drive it in a few. While I had it in the garage and was freed up for an hour, I ran a KOEO test. I got these first two codes 67, (I don't have my A/C compressor on, and 84 (EGR vent fault). Not sure if that refers to the EGR solenoid or...??? The EGR valve has 8K on it, so it's fairly new. The interesting code is the stored memory code, which is 33. That is EGR not closing properly? This does have the feel of that. It seems the best thing to do would be to take the EGR valve off and apply vacuum to check for free movement???

Pressed for time here, so trying to get it right the first time. I am driving the truck by feathering the gas when I come to a stop and holding it at an idle. Interesting way to drive...

Tony

 

With engine warm and idling, check if there is vacuum on the EGR Valve hose, there shouldn't be, EGR valve is only used when accelerating or when engine is under load
Plug the end of the hose and drive it to see if engine still stalls
Yes if EGR valve is partially open when slowing and stopping engine would stall
84 has a few meanings all related to EGR system and solenoid

33 is EGR, but the sensor showed Valve didn't open as directed by computer every time, which could also be solenoid issue as well

67 is Neutral switch fault, in your case clutch pedal switch

 

First time I've had more than a few hours to work on the truck. I took off the EGR valve and tested it with the mitey vac. Diaphragm held vacuum and the pentil moved. Re-installed EGR valve. Put the vacuum gauge on the outlet that goes to the red (vacuum box) port. I have 14 pounds. The green vacuum lead from the EGR relay isn't pulling vacuum at idle.

Time to drive truck. The truck was already warmed up when I'd taken off the EGR. I start it up and it idles fine. Starts to miss a little bit after five minutes or so. Then I drive it and I get about half a block; and the 650 RPM or so doesn't hold; the truck loses idle and stalls. I've got so many new sensors and electronics, I just can't figure this out. The only sensors I haven't replaced are the temp sensors. I have no major vacuum leaks that I can hear. Just can't figure it.

tony

 

Ran some codes. Code 18 came up, related to SPOUT. Now I'm digging into this.