90 F250 Rough Idle?

[billrigsby]

My 1990 F250 129K has developed a rough Idle. I did the standard tune up (plugs, wires, cap rotor, air filter) Fuel filter was done 03/09 and I have 40psi fuel pressure. No CEL but I get a code 12 (unable to maintain idle during self test). I do sense a rich runing smell during idle. I was thinking EGR Valve but I hate throwing parts at the thing. Seems to run OK at speed, but I have not had it on the road, just up and down the long driveway. When I first start it cold it will die with out throttle, once warmed up I have the bad idle. Go to WOT and let off usually will die with out throttle help.

 

[5.0Flareside]

IAC-Idle Air Control valve.. sounds like it to me.... wont hold an idle if the IAC aint working very well..

did you do the code test when the truck was warm?

 

[billrigsby]

Yes truck was warm, I'll check ito the IAC Valve,
see if I can find a test procedure, only have a Chiltons.

 

[Fordzilla80]

IAC could just need a cleaning. I'm having a similar problem with my 03 Ranger. It didn't like stoplights at all, it kept trying to fall under 500 rpm and die unless I manually held it at 750. I cleaned the IAC, as well as the throttle body, and it's still running a little rough, but it hasn't died since, and it holds 500 on the tach by itself. You can clean the IAC with some throttle body cleaner. There's two bolts holding it on, and a connector.

All in all, sensors suck.

 

[Ridgerunner]

I agree IAC but cleaning is a temporary solution. You will need to replace it eventually a New one runs about $60.00 if you shop around. Also try Rock Auto their prices are good also.

 

[Fordzilla80]

New one runs about $60.00 if you shop around.

And that's exactly why cleaning is usually the first thing mentioned.

 

[Ridgerunner]

And that's exactly why cleaning is usually the first thing mentioned.

But it is only a temporary fix,which is fine for a few trips. If it's a daily driver the cleaning won't last long. Ask me how I know????

 

[billrigsby]

Well I took it off and removed the solinoid, it moves freely and has no carbon build up to speak of, the resistance on the solinoid also checked out good at 9.7 ohms. Seems the problem is getting worse, now I have some popping like a slight back fire?

 

[Ridgerunner]

What size engine?

 

[billrigsby]

5.8 liter V8

 

[Ridgerunner]

Have you checked your timing?

 

[billrigsby]

No, but what would cause the timing to change overnight?

 

[billrigsby]

Also with the TFI-IV ignition system I thought there was no adjustment The ECM took care of that?

 

[Ridgerunner]

No, but what would cause the timing to change overnight?

With over 100,000 miles the chain will stretch,or the timing gear will start stripping. Might be best to post more info on what you have done. If you do need to replace the timing gear spend the extra $$$ for a good name brand and get one that is pre emissions 72 and back it will give you some extra power. The more info you can post some one can help you get it figured out.

 

[billrigsby]

If by what I have done you mean mods, it is bone stock?

 

[Ridgerunner]

If by what I have done you mean mods, it is bone stock?

No I mean what have you done as a tune up? If it was running fine before then it could be the type of plugs used, plug wires.rotor button dist cap, stuff like that.

 

[billrigsby]

No, the tune up was done in responce to the problem, plus it was probably due for it.

 

[Ridgerunner]

I know the ecm is obd1 and it does control the timing along with emissions. I would put a timing light on it and check to see if it is out.

 

[billrigsby]

I can try that but as bad as it is running, not sure it will be accurate

 

[flareside_thunder]

Make sure you pull the spout connector when you check the timing...stock setting is 10* BTDC. I'd still clean the IAC regardless, better yet...unplug the harness from the IAC and start it up when it's cold......if it will sit there and idle good then chances are, that's your problem....also, check the voltage at your TPS.