OK,

I posted about this problem before, but still can't find a solution. I've got a 1987 Ford f150 4.9L - it won't idle/stalls out unless you play with the throttle. So far we've replaced dist. cap, wires are like new, tps , egr valve - and it still won't stay runnin'.

With a digital multi meter we've tested IAC and it reads 10.3 ohms, and a manual said it has a required value of 7-13 ohms, so we assume it's working. We've also tested the EGR position sensor and it read 4000 ohms dropping as required when activated.

So, what the hell should I do now? We've replaced everything we've been 'told' to replace via this forum, and it still ain't running. Any advice?

 

Have you checked to be sure that voltage is reaching the IAC? Thinking along the lines of a failure in the circuit or the computer not sending the right level of signal. Not sure what the test procedure is, or what the recommendation ranges are.

Is it running rough, or just slow?

Don't adjust the butterfly set screw to get the idle speed up.

 

Have you checked the computer for codes? The only time my '87 had a bad idle it was the IAC. You may want to clean it.

 

check out this post. https://www.f150forum.com/f10/another-start-idle-question-10814/ .i had the same problem. good reading on the IAC. cleaning it has solved my problem.

 

ok,

well, I had already taken off the dist. to check the ICM, and because of how terrible they looked I just went ahead and bought both new ..... but now I am having trouble getting the dist. back in time (didn't know it had a 'time') so I havent been able to start the truck and see if this was the problem.



next I will attempt to clean the IAC if this doesn't fix the problem. I guess I'll let you know.

 

also, me and my friend found this plug, and neither of us know what it is, or where it goes ... and we can't really find a plug near it. anybody have an idea?

http://www.4freeimagehost.com/show.p...d235277785.jpg

 

Good morning, will try to keep my instructions as simple as the job is. Remove #1 spark plug. Very most forward plug. Follow that plug wire back to distributor to confirm its position on distributor cap. Original caps have a #1 at the correct tower. As you turn engine over manually, listen or feel for air expelling out of plug hole, this is compression stroke, continue turning untill the 10 degree mark lines up with pointer. Holding distributor, rotate rotor untill pointing to #1 tower, install distributor. If it won't go in all the way, it hasn't engaged oil pump shaft, simply rotate engine slowly by hand and keeping a very light pressure downward of distributor. Recap, #1 piston at 10 degrees of compression stroke, rotor pointing to #1 tower of distributor cap, install. Reset timing with timing light after engine is running. Just seen your additional thread, plug looks like an air conditioner connection. Remove air intake for easier assembly of distributor.

 

I have the same truck and the same plug which isn't plugged into anything. As Bill said it is the a/c compressor plug. Basically, to keep costs down the factory makes one wiring harness for all the same year trucks and anything your truck isn't equipped with doesn't get plugged in.

 

I have replaced distributor, coil, ignition switch, egr, iac, tps, truck is now not starting would bad plugs cause no start or only rough run.

 

I was afraid of this. Every time an engine won't start after the distributor is removed is, because it is put back in on the exhaust stroke, not the compression stroke. Again trying to be brief which I can't as my prior post prooves. It takes two complete revolutions of the crankshaft to complete all of the 4 strokes necessary for an engine to run. 1/2 turn of the crank is intake stroke. 1/2 turn of the crank is compression stroke. 1/2 turn of the crank is power stroke. The last 1/2 half turn of the crank is exhaust stroke. Again find 10 degrees BTC of intake stroke and look at the rotor, its probably pointing to #6 cylinder tower. The crankshaft makes two revolutions to the camshafts one. The distributor and camshaft go at one haft crankshafts speed. Hope this helps. Now you know why I'm a mechanic not a teacher.