Strange running symptom?

[twobone]

Hi. My 96' 400 runs fine when cool. I just cleaned the stepper motor which was also loose, so now all good there. Once it gets warm (fan kicking in) though she runs rough in the lower Rev range. Shudders and not sweet up the Rev range.

I wonder if it's vacuum or something. When warm she has a very choppy idle which sometimes clears a bit: the idle will come up a bit and I can feel the brake booster "puff up" and the brake pedal comes closer.

I will check the distributor vacuum line tonight and perhaps remove it and block up the vent to the intake.

I think the Bosch I coil is pretty new...but could that be the issue?

Maybe the temp sender?

Any thoughts greatly appreciated. Like I said, when cool in the first 20 minutes of driving she runs like a champ.

[Classic Chim]

twobone said:

Hi. My 96' 400 runs fine when cool. I just cleaned the stepper motor which was also loose, so now all good there. Once it gets warm (fan kicking in) though she runs rough in the lower Rev range. Shudders and not sweet up the Rev range.

I wonder if it's vacuum or something. When warm she has a very choppy idle which sometimes clears a bit: the idle will come up a bit and I can feel the brake booster "puff up" and the brake pedal comes closer.

I will check the distributor vacuum line tonight and perhaps remove it and block up the vent to the intake.

I think the Bosch I coil is pretty new...but could that be the issue?

Maybe the temp sender?

Any thoughts greatly appreciated. Like I said, when cool in the first 20 minutes of driving she runs like a champ.

Any one of those basically, sounds similar to temp sensor issues but don’t quote me on it. Could be coil once hot!
Rovergauge might be the best tool here before moving on to new parts.

[ed_crouch]

Usual suspects: Coolant temp sensor might be telling fibs, probably worth checking throttle pot incase its incorrectly triggering WOT enrichment, and the ignition amplifier is a potential cause too. I would be quite suspicious of the ignition amp if its only bad when hot. Smacks of decaying electronics.

[WOO5IE]

Could also be the plug extenders.

Notorious especially when getting a little warm.

Try running without them and then get rid. You will need plugs with built in resistance.