Well, before it began to get really cold, I thought I was on the right track regarding the stumbling idle on my '89 302.

Yesterday the temp dropped to about 10 F with a strong wind. When I started the truck first thing in the morning, it fired right up....then died. I started it again, and it fired up and died. Next time I held the pedal down and it fired up and I had to feather the throttle for about 5 mins in order for it to idle on it's own. I have no fast idle.

To re-cap, I have washed/flushed the IAC until the TB fluid ran clear and verified voltage to the harness. It almost seems that it is 'sticky'. Once the truck is up to temp, she runs great.

Any ideas where to look now?

Dan

 

Check your MAP sensor it measures the barometric pressure and controls your fuel.

 

Disconnect your MAP sensor and try to start it, if it runs fine for a minute, chances are it is the MAP. Check your codes before you buy anything.

 

check your air tubes going into the TB they could have a hole or deteriorating around the TB. Mine did this too and that's what was wrong it.

 

I swapped a used MAP sensor and didn't notice much of a change, so I decided to put the original EEC from the truck back in. I had swapped it for an EEC from '92 302 back when I first bought the truck and was fighting certain drivability issues.

The idle at start up is nice, about 1500 rpm and slowly settles in at 750-850 after a minute or so. Throttle response seems better and I don't have the spark knock anymore.....

I seems to think I caused many of my own problems by swapping parts around!!! Oh well, being 42 years old means when you screw up, you have the ***** to own up to it!!!

I will keep all posted how it performs over time.

Dan

 

Well, the trucks performance last night was not as good as I first thought. I decided to start it before leaving for work this morning and it acted the same way as it did previously- starts right up and dies. I have to feather the throttle in order to maintain idle speed. So, fast idle at cold start up is not happening.

Does anyone know the layman heirarcy of the ECT and ACT as it relates to the EEC at cold start? I have always thought that a duff ECT would cause a Ford to run rich (flood) at startup. Based on that theory, I am now wondering if the ACT is the culprit. I have not checked codes since re-installing the proper EEC, perhaps that will shed light on the situation.

And the troubleshooting continues......

Dan

 

I know this may sound weird but is there anyway your spark plugs may be gapped wrong or your distributor damaged. Other than that idle speed?

 

Looked it up heres what i got:

1 loose or faulty connections at dist. coil or alternator.

2 Fault in fuel or electrical system.

3 Insufficent fuel reaching carb.(check fuel pump)

4 Vacuum leak at the gasket surfaces of the intake manifold or carb/throttle body.

 

I never had an opportunity to really delve into more troubleshooting last night, altho I swapped the original MAP back in, and the problem continues.

I back probed the IAC harness and had 11.4volts on 1 pin and nothing on the other (EEC signal I suspect). That was concerning. No wonder the IAC isn't working, it isn't recieving the signal to cycle.

Now, what sensor(s) supplies input to the IAC....HEGO, ECT, ACT or are both EECs I tried crapped? These are the questions I am asking myself.

Once the truck is up to temp, the IAC works....meaning, if I unplug it while the truck is running and warm, the idle drops. As well, if the truck is idling warm and I unplug the ACT, the idle speed increases, which idicates to me the EEC defaults to worst case, and causes the IAC to cycle at 100%. Me thinks the ACT might, and I only mean might, be the root. Am I diving too deep here, or is there an easier way to go through this?

Again, if there are any EEC guru's out there, I would appreciate you chiming in. I am especially interested in finding out the base heirarcy for sensor (ECT, ACT, HEGO, MAP.....) input in the EFI logic of the EEC.

Cheers, Out

Dan