1995 GT 5.0 Surging- idle to 4k RPM

95gtSteve · Feb 25, 2013

Hello group!!!

No MIL light.....

Well finally got the rubber tank/filler neck seal in, can fill up now, YEAH!

So, Sunday (2 days after the filler neck) Sally begins to surge at idle, not much, but noticeable. I can feel vibrations from the engine all the way to 4k, which is my normal shift daily driving. Serious shakes...

New plugs, wires, gold cap/rotor. 'zone tells me fuel pressure. Remove the vacuum line from the regulator, radical change as I expected. Rule that one out. Pop a small screwdriver down the fuel rail valve- GOT PRESSURE!

Ok, lost now, acts like the dampner is toast, but nope, it's solid. 180k miles, did my cam go flat? IAC has been bypassed....long story...

I went to the 'zone today and warrantied new plugs and wires. Same result. Shakes at 2k like crazy....I can see motor mounts in the future....

Anyway, I just replaced the tank filler neck seal 4 days ago. Ran like a raped ape Saturday....85-90 no problem, get some rubber out of 1st. Overnight it went nuts. Checked for vacuum leaks, loose connectors, etc. Possible Ignition Module or maybe a I jumped a tooth on the timing gears? ICM?

I'm stuck.....throw me a bone!!!!

CC'S95GT · Feb 25, 2013

If the HB is origional then it's due for replacement anyway. Waay overdue.
Do you have any mods to the motor?
You might need to do a base idle reset.
Also if you have a multimeter test the TPS for dead spots.

95gtSteve · Feb 25, 2013

CC'S95GT said:
If the HB is origional then it's due for replacement anyway. Waay overdue.
Do you have any mods to the motor?
You might need to do a base idle reset.
Also if you have a multimeter test the TPS for dead spots.

CC- The only mods are an MSD Street Fire coil and CAI. I have a code reader on it's way....

Don't want to sound like an idiot, whats the HB? And how's a base idle reset performed?

180k miles....

Thanks,

Steve

EF5.0 · Feb 25, 2013

Harmonic Balancer I believe.

Base Idle can be reset by following these directions: http://sn95forums.com/showthread.php?6691-Fixing-your-SURGING-IDLE!!!-IN-HERE!!!

RichV · Feb 25, 2013

HB = Harmonic Balancer, it's what balances the motor.

Does the shake get worse with RPM? Or is 2K the worst of it?

If the HB slipped, it would shake all the way to redline. If it's ignition related, it could just be a specific RPM when it's acting worse. Also fuel pressure needs to be checked with a gauge, a screwdriver in the schrader valve won't really do anything. What happened when you removed the vac line off the FPR? You should not get a drastic change of anything.

95gtSteve · Feb 25, 2013

RichV said:
HB = Harmonic Balancer, it's what balances the motor.

Does the shake get worse with RPM? Or is 2K the worst of it?

If the HB slipped, it would shake all the way to redline. If it's ignition related, it could just be a specific RPM when it's acting worse. Also fuel pressure needs to be checked with a gauge, a screwdriver in the schrader valve won't really do anything. What happened when you removed the vac line off the FPR? You should not get a drastic change of anything.

Rich; the shake is at idle to redline.....ran a quick code test- 563, High Fan, which I knew. Have a new HB on it's way from LMR...

It's my last option!!!

Steve