SSinister11x

Ok Fbody pals, I've got a 96 lt1 that is having some idling issues. When the car warms up after bein on the road for awhile (25 mins or so) i'll put it in neutral and the idle will go from 1600 to 2500 RPM up and down until I slow the car down to about 5 mph, then it will go to normal idle at 900 RPM. I get up to speed and there the idle problem happens again. What sensor causes the car to idle in regard to wheel speed? I replaced the TPS and the IAC sensor and put a new gasket on my throttle body. What other possibilities could be causing this nonsense? Any input is greatly appreciated.

SSinister11x

Is there some other sensor that would cause this? Should I be looking into a vacuum leak somewhere? Really frustrating.

ACE1252

Are you sitting still when kicking it into neutral or moving at a certain speed? Still stock heads and cam?

SSinister11x

No, for instance if I'm crusing at 30 in 3rd and put the clutch in, the rpms do this. Only time it will stop is if I roll to almost a stop. LIke 5mph or maybe less. I have stock heads and cam yes.

ACE1252

Oh, so you are just driving, clutch in to change gears(foot off gas too), and the engine rpm surges?

SSinister11x

Yep, happens at any speed above 5. I can kinda feel the surge even when clutch is engaged.

ACE1252

Factory manual mentions checking for vacuum leaks, check MAF sensor for problems, check the grounds straps for good connections, fuel pressure check, O2 check as well.

It would be interesting to see what your IAC counts are at idle.

Have you verified your TPS voltage with the throttle closed(0.67V if I remember correctly)?

No SES light correct?

SSinister11x

Nope, no check engine light. When the engine is warmed up is when the problem occurs, does that narrow down my possibilities at all? I do think that my fuel pump is going out. The fuel pressure is at 40 when the key is on and it quickly goes down ( bad check valve)? Ground straps, is that the one coming off the ignition module?

ACE1252

That is one strap. There is another ground connection on the passenger side of the block near the knock sensor and the connection for the battery ground around that area too.

I would check for vacuum leaks first. Check the condition of all your hoses. That is the reason for checking the IAC counts. A low count number(I think it is low) would indicate air is getting pulled from somewhere other than the IAC passages. The IAC may be able to compensate for it at low flow, but when the flow gets higher it can't.

SSinister11x

Thanks for the help man. How do I check the IAC counts?

ACE1252

You'll need a scan tool or scanner software for that.

GCEZ28

Ok. Your car is doing EXACTLY what my car has done TWICE in the past. Mine is an automatic and had to put it in neutral at every stoplight. Could not drive it in the rain. Never threw a code.

OPTISPARK.

Just replace it. Problem solved.
I might suggest an MSD. Just be sure the seal in the timing cover behind it is good. Mobil 1 and the distributor don't get along.