Hey gang,

I have posted a few times regarding the transmission in my 95 psd and its problems as of late. A little background: Recently, after the truck gets good and warmed up, the tranny shifts funny. Normally (when cold) shifting from park to drive, you can feel the truck lurch forward having to hold the brake to keep from moving. When warmed up, it dosnt always have the lurch forward, sometimes rolling backward if on a grade, ans you'll have to rev it to about 1800 RPM to get it to move. Like the TC is unlocked. I got a reply a while ago from Mark the tranny guy and he suspected forward drive clutch seal failure. Thinking I have to get a rebuild , I started looking for a less expensive option. I found a few threads when the OP stated unplugging the ICP made a big difference in his truck shifting.

Yesterday, I had to replace the front brake rotors and pads. Went smooth. After back together I took the truck for a short drive. I noticed, after I returned, that the idle was wierd. It will sit at 650 then drop below 500, chug a bit and back to 650. Ive noticed this before but never did much about it. Last night I unplugged the ICP plug and woah...The idle tightened up, no chug or anything and stayed right at 650. So, I am wondering if the ICP has been my trans issue from the beginning. I haven't driven it very far since uplugging the sensor, but plan to this weekend.

 

I doubt it. If the engine was under powered it can cause shifting issues but the ICP has nothing to do with gear engagement

 

If the TC were locked the truck would stall. I guarantee the TC is unlocked as it is supposed to be.

Fix whatever is wrong with the engine before fixing anything on the transmission. An engine problem WILL cause transmission issues.

 

Mark can a engine issue cause you to have to rev to 1800 for gear engagement ?

 

I've never seen that happen. That may be the trans, but one should ALWAYS fix any engine problem before attempting to fix any transmission problem.

 

Unplugging the icp sensor smoothed out the idle but driveability sucks. Very hard shifts. I plugged it back in for better manners, but it has a noticable miss while driving. So is this part still bad if it improves idle?

 

Yes. If it idles better unplugged then you should Change the ICP.

When its unplugged it defaults to psi. Basically the PCM takes a wild azz guess at what ICP should be.

 

Yeah, replace it. Usually when any vehicle runs better when you pull something like that it's because the part is so bad that the engine prefers the computer just giving it a guess to the actual values it is receiving. But accurate info is always better.

And a word of advice that I learned the hard way? When Mark tells you an E4OD is about to cost you a lot of money, he was right. He diagnosed two of my tranny problems, both bang on, first time I searched high and low for an alternative option, should've just called the wrecker then and there, would have saved me a day of waiting.