HELP....high idle and dieseling!!

[FordExplorer18]

I have a 1992 explorer with 105k on it. Ive had it for about a year. for the past year when I put it in park, after driving for a while, it revs up to about 1800 rpms. When I shut it off it will diesel for about 1 minute then die.

I have replaced the IAC, the computer, had it checked for leaks with propane and cleaned the engine for carbon build up, Ive checked the throttle cable and I am still having the same problem.

Does anyone have any other ideas as to what could be causing this?

Thanks

 

[Electrohacker]

105k... time for a tune up!

 

[Billy177]

get a tune up the dieseling is likely cause by carbon deposits creating hot spots. nothing seafoam can't fix

 

[FordExplorer18]

Tune up, as in what? I have done the plugs, wires, fuel filter, air filter and regular oil changes. I have also done seafoam 3 different times.

 

[Billy177]

try cleaning the maf then. try driving it hard from a few stop lights letting the rpms get high to blow out some of the carbon also try cleaning the throttle body

 

[EBInterceptor]

The high RPMs with help burn some of it out, but I don't see the TB being an issue.

 

[Billy177]

it might stick partially open causing the high idle

 

[FordExplorer18]

Well I have cleaned the MAF and everything. Like I said its been almost a year I have been trying to figure this dang thing out. Is there anything else that controls the engine besides the computer and the IAC? Could it possibly be something wrong with the fuel injection? (on a side note, it doesnt diesel or idle high when the IAC is unplugged) but i have purchased 2 new IACS so I know they are not causing it.

 

[EBInterceptor]

I posted all the things to trouble shoot in the other thread about dieseling. Could be an EGR system or low idle. Don't know about the high idle causing the dieseling, but I understand that a stuck throttle would cause the high idle.

 

[Billy177]

there is also the tps

 

[gss]

Have you checked for a vaccum leak in the tranny? The dieseling is caused by fuel still flowing into the hot cylinders and burning, you will eventually blow the engine because the dieseling is causing the engine to try to run backwards. I am not a mechanic by any means, just my line of thinking. I could be all wrong?? Advise is free.

 

[FordExplorer18]

there is also the tps

I thought it could be that as well. I tried replacing that at first. It didnt change anything so I returned it and put the old one back in. I am really becoming stumped here.

I havent checked for a vacuum leak in the tranny though. If that in any way tied to the IAC?

 

[FordExplorer18]

Another question.......I just remembered that 1 week after I bought the truck I did the plugs and wires. Is there any chance that maybe a wrong gapping or wrong type of plug could cause it to diesel?

The plugs I pulled out were motorcrafts. I put in Autolites but i did not check to see if the heat range was the same.

 

[Billy177]

you may have gotten the plugs for the sohc. they are longer and could very well eb creating the hot spots and causing the engines to run like crap

 

[FordExplorer18]

Well I went to autozone this morning and got motorcraft plugs(the right ones for my year) gapped them right and put them in. I am still having the high idle and diesel problem.

Here is what throws me off.......when it is idling high, I unplug the IAC and the idle goes back down to about 800. I have replaced the IAC 2 times and it is still doing this.

Does anything else control the IAC besides the computer?

 

[Billy177]

hook up a vaccum gauge and do a test, that should tell you

 

[FordExplorer18]

I went to the dealer to ask them if they see a common problem with this year of explorer. He said that 92-96 have had a lot of problems with the gaskets on the intake manifolds leaking. So now I am in the process of putting new gaskets in the upper and lower intake manifold. Hopefully when I am done this will fix it.