1991 3000GT VR-4 is hesitating at 3000 rpm. Any ideas?

Jun 07, 2004 3 Replies

Hi all, For about a week now, at different rpms, at low throttle, my car hesitates or stutters very badly, as if I were accelerating and stomping on the brake at the same time. It happens at anywhere from 2500 rpm to 3000-3500 rpms, in first through third gears. It only happens if I hold the throttle at those rpms - if I mash the gas, it will roar through it and not stutter. The other thing, if I am idling and I steadily raise the rpms through that 3500 mark, it doesn't stutter. I also notice that it only seems to happen when the car has been running for awhile and is warm.



I have an HKS VPC and GCC hooked up, and I think I have them properly tuned, that is, I'm not running too rich or too idle, according to the readings I get on the GCC. (If anyone has the manuals to either of these, I'd REALLY appreciate getting a copy of them, and I'll pay for 'em, too. My mechanic won't touch that stuff without the manuals). The car recently was dying at idle, so I had the ICS (stepper motor) tested and found that it's bad, so I'm having it replaced. Would the ICS have anything to do with this new and very irritating problem? I also bought some fuel injector cleaner, haven't tried it yet, though. Thanks for any and all help or suggestions!



Al



1991 3000GT VR-4

Hi all, For about a week now, at different rpms, at low throttle, my car hesitates or stutters very badly, as if I were accelerating and stomping on the brake at the same time. It happens at anywhere from 2500 rpm to 3000-3500 rpms, in first through third gears. It only happens if I hold the throttle at those rpms - if I mash the gas, it will roar through it and not stutter. The other thing, if I am idling and I steadily raise the rpms through that 3500 mark, it doesn't stutter. I also notice that it only seems to happen when the car has been running for awhile and is warm.

I have an HKS VPC and GCC hooked up, and I think I have them properly tuned, that is, I'm not running too rich or too idle, according to the readings I get on the GCC. (If anyone has the manuals to either of these, I'd REALLY appreciate getting a copy of them, and I'll pay for 'em, too. My mechanic won't touch that stuff without the manuals).

The car recently was dying at idle, so I had the ISC (stepper motor) tested and found that it's bad, so I'm having it replaced. Would the ISC have anything to do with this new and very irritating problem? I also bought some fuel injector cleaner, haven't tried it yet, though.

Thanks for any and all help or suggestions!

Sounds like a fuel mix problem. Probably too rich since you ate the ISC. I would get a logger and properly tune the mix.

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