RPM's bouncing at idle, please help

[dsl_pwrd_ford]

at idle the rpms will bounce 50-100 rpms in either direction. this morning they were going so low that it sounded like it was going to die. What would cause this? It's only at idle. probably not fuel cause it's been happening for awhile and i've filled at different stations. Maybe filter? i'm due in 2k+ miles. It's getting annoying.

[sldghamr]

i had the same problem with my 96er about a year ago. ended being my IDM was dying.

[dsl_pwrd_ford]

what does IDM stand for?

[dsl_pwrd_ford]

nevermind, i got it. how much do those run? a friend also mentioned a possibly bad IPR

[sldghamr]

the OBS version is about $1100 at the dealer. you can probably pick one up at your local wrecking yard for a lot cheaper. i was told by the mechanic who changed mine, this part is Ford only, the IH version will not work. you might also look the ICP sensor, $100 at the IH dealer (which does work in our trucks, i am using the IH version myself)

[elibenson]

They are available online as reman units for a couple hundred bucks. I bought one from a place called "auto computer exchange" or something. I found it on Ebay, but the company selling it was auto computer exchange. Obviously they wanted the old one back.

While you are changing it (if that is indeed the problem) you might want to get one from a newer truck. The voltage is higher on the new trucks (120 or 110 vs yours at 100). It makes your fuel injectors snap open quicker, which advances the timing a little. Gives better throttle response and a little bump in power.

The ideal about the IPR is also a possibility. If you have a scanner, you ought to check your IPR% and voltage while it is running. Also check for codes. IDM problems throw some codes that might tell you if it's going bad or not.

[dsl_pwrd_ford]

i used a code reader from a parts store and it gave NO codes, so prolly not the IDM then?

[elibenson]

It's hard to say. The IDM might think it is still working fine, when it not. If you have any friends with powerstroke trucks, you could borrow one of theirs and try it for a few minutes. It's a 5 minute job to pull one out (3 8mm bolts, and one 10mm on the electrical connector). I know it's not a really scientific test, but it would be easy.

[sldghamr]

Originally Posted by dsl_pwrd_ford

i used a code reader from a parts store and it gave NO codes, so prolly not the IDM then?

maybe, maybe not. it's my understanding that the ICP sensor can cause your symptoms and is one of the more common problems with the 7.3L. i personally would start there. far cheaper fix than the IDM.

[elibenson]

You can test whether or not it's the ICP sensor by unplugging it. It will run without it, but it will be a bit jumpy. If the idle smooths out, then that might be your only problem. Also, check for oil in the electrical connection. If there is oil there, then the ICP sensor needs to be replaced any way. Also, if there is oil in there, that could be causing your problems.