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Here's something that happened earlier today, and happens every now and again.

My fiancee was driving, and had to gun the car across traffic from a stand-still. For a second it shuddered horribly, the whole car jumping up and down and sounding like the inside of a bass drum being hit hard and repeatedly. It did this again later on when she gunned it again from a very low speed, at or less than 5 mph. Both times the car was going from zero throttle to quite open throttle, as she drives much more, er, spiritedly than I do. I've noticed this shudder before when I'm driving, too. It happens in a straight line, and when the wheels are turned. And only when the engine is in a near-idle-RPM high-load condition, and goes away when you back off the throttle. Rolling into the throttle instead of stabbing makes this non-existent.

The transmission filter and fluid were recently changed, cooler hooked up, and the fluid was changed a year previously also. I have new NGK plugs and a new Denso O2 sensor installed. Wires were changed a year ago with Autolites. Coils and ICM are original. Intense PCM added in August 08.

I searched for "shudder" and found a few posts about ignition possibly being the cause. And a few about transmission being the cause.

So the $64,000 question: transmission or ignition?

I used to have a shudder and a tune-up and transmission service solved it, however it was only minor. I am no gearhead and I am sure they will chime in but a shudder that bad to me would be the transmission. But thats only my guess....

I used to get something like that as well. Oddly enough when I got a mail-order PCM it went away. It could have something to do with your current PCM setup. I think the dealership or someone with a tuner could update it. I'd try that before doing anything expensive.

The first thing to ask, was any work done on it just before it started doing this? Does it throw any codes? Another thing that has me wondering is, does it only happen when the wheels are turned or when it is going straight too? If it is only when the wheels are turned, you could be seeing an early failure of a CV joint in one of the axles.

Otherwise, Test your coils according to Techinfo and pull the plugs and inspect them and possibly get a new set of wires. A lot of people here recommend the Belden wires from Napa. That is what I run and I am pretty happy with them.

No codes, no stored codes. The plugs are only a few months old. And the wires a year old. It happens when the wheels are straight.

The fuel tank sender and pump were replaced last September, along with the PCM.

Looks like I'm testing some things later this week.

Pull the plugs and see how they look. Check the gap and post pictures. Check the coils though, primaries and secondaries.

Try cleaning the MAF sensor w/spray MAF cleaner (NOT carb cleaner!). A dirty one will cause a nasty dead spot right off idle, mainly when "stabbing" the throttle hard. It's not as noticeable with a slower acceleration.

The two little wire looking things in the hole are what need to be clean (very delicate)

Is it possible that it's the fuel filter?

My thoughts are the fuel pump getting weak or perhaps the pressure regulator being slow to react.

In my experience, a tranny shudder comes on when I rolled into the throttle. When I mashed it, there was no shudder. Although it could just be a different failure mode, I suppose.

The pump is new as of August 08, I've cleaned the MAF recently, and the plugs were recently changed.

The fuel filter is original. The line is very rusty, so I've not been able to replace it. A mechanic might have a different opinion.

To update, cleaning the positive battery terminal led to more voltage, and more consistent voltage.

I tried reproducing the problem, and it didn't occur. So it is likely voltage-related. Next I'll check the coils.

LeSabre in Buffalo wrote:To update, cleaning the positive battery terminal led to more voltage, and more consistent voltage.

I tried reproducing the problem, and it didn't occur. So it is likely voltage-related. Next I'll check the coils.

My guess would be the transmission is slipping and catching. Think back to see if it occurs most when the transmission is really good and warm.

I gave it over half throttle from a dead stop a few times with the transmission warmed up after driving lightly for half an hour, and the only effect was chirping the tires.

And a 60k mile transmission? I've serviced it twice in a year's time, once at 35k, the next time at 60k miles, so neglect is not the issue. Could be a dud, I guess.

More testing needed.

LeSabre in Buffalo wrote:I gave it over half throttle from a dead stop a few times with the transmission warmed up after driving lightly for half an hour, and the only effect was chirping the tires.

And a 60k mile transmission? I've serviced it twice in a year's time, once at 35k, the next time at 60k miles, so neglect is not the issue. Could be a dud, I guess.

More testing needed.

Well I have a Goodwrench rebuild thats a year and 4 months old that sounds like a grinder!!!

Point.

I tried again today, and nothing. Couldn't get it to shudder, but something didn't "feel" right. I need to add some hill starts into the mix. And test the primaries on the coils. The secondaries all were within spec.