icm update

[SteveT]

Sorry if I restate an old column , but a search of the forum did not answer my question.  As part of getting ready for my West Coast trip , I replaced my coil assembly last week as it was oozing a bit.  I used a new Delco ICM and coils for a 91 , and replaced wires and plugs at the same time with Platinum plugs and premium wires.  Car starts much better , has better throttle response , but once I am above about 60 mph I have a terrible stutter under constant throttle or decelerating.  Under cruise the car shakes horribly.    Checked icm plug and pins , no visible issues.  With son going into icu this week I have been shaking my way back and forth until this morning , reinstalled original icm/coil and shake gone.  I was under the understanding that these were interchangable through about 94 model.   Any suggestions?  Cant afford to buy a second new icm and have it not work.

[DAVES89]

They are interchangeable with the starting and low speed operation. I would return the ICM to the place you purchased and try again. What you are describing with the shudder is more common to the Mass Air Flow sensor

[padgett]

That is almost a classic low rpm/moderate load misfire and from your description a bad coil, ICM, or connection (14 pin connector has short pins). I would begin by measuring  the three coils primary resistance since almost no one has a scope any more.

[SteveT]

old icm running fine , it is not low rpm , but at cruising speed only at constant throttle or deacceleration. pins and plug all good , i will returm icm

[SteveT]

and coils all test out good

[Ronnie]

1 hour ago, SteveT said:

it is not low rpm , but at cruising speed only at constant throttle or deacceleration.

 

The only thing I can think of happens under those conditions is the EGR valves cycle open and closed. Do you have any codes in diagnostics?

[SteveT]

just my 041 that I have been procrastinating about.   Guessing earlier comments about the icm must be correct.  coil packs check out ok , and problem goes away with old unit

[padgett]

Meant at about 50 mph and in OD cruise but I do not understand why it would miss on deceleration.. However if goes away with old ICM, there you are. Sometime things are bad off the shelf (and maybe why the are on the shelf in the first place).