Hi, I'm new here. Thanks in advance for anyone willing to offer me any advice as it is greatly appreciated.

I have an '88 F250 7.5L V8 EFI 4x4 manual.

I've been having problems with rough idle (especially when cold) and when I rev the engine then take my foot off the gas the engine will almost stall, then catch itself and rev back up, or sometimes stall. I also had a problem with a bit of hesitation (revs dropping before rising) when applying gas, but replacing the TPS took care of that issue.

I still have a rough idle most of the time (engine shakes and sounds like some missing occurs and feeling the exhast w/my hand confirms the missing) and as the engine returns to idle it stalls or almost stalls. I've noticed that if I barely (and I mean REALLY barly) apply gas and hold it there the tac will bounce between 1,000 and 1,500 and will continue doing this until I remove my foot from the peddle or depress it further.

I've tested my IAC with a volt/ohm meter and it's receiving the proper voltage and it's internal resistance (ohms) are within spec (per the internet). I removed it and verified that it moves freely and the plug is tight (well, at least I can't blow any air past it when put to my mouth). I cleaned it (a bit) w/wd40 (not sure if this was the best idea, but it didn't have any affect).

I removed 1 spark plug and compared it against a list of images of spark plugs with varying symptoms, but it looked just fine, not even worn enough to replace. I've not tested the cables or looked at other plugs.

My gut feeling is this is due to some sensor, but I really don't know much about vehicle mechanics other than basics (but I'm a quick and willing learner).

My dad gave me this truck and I really like it, but I really don't use it enough to justify handing a mechanic $1,000 or more to fix it. If anyone here can offer some advice of things to try or sensors to test I'll really appreciate it as I have no idea where to start other than buying and replacing things unneccessarily.

Thanks.

 

Ford Fuel Injection How To Run a Self-Test


best place to start and let us know the results

 

Nice to know this can be done w/out a reader as mine won't deal w/older cars/trucks. I had the battery unplugged for a while today while working, but have driven about 15 miles since then. How many warm-up/cool-down cycles do I need before codes will be available?...or can I read them tomorrow?

Thanks for your quick response. I'll be sure to let you know any codes I find using the instructions in you link.

 

i dropped a new ecm in mine and after 2 warm up/cool downs i was pulling new codes and lost my old codes, so i would say 2 cycles would be enough to get codes again