90 ZR-1,hesitates,stumbles,erratic idle

vette punk · 05-02-2005, 05:56 PM

We just had a customer bring in a 1990 ZR-1 that stumbles,hesitates on acceleration. Idles up and down and will stall. Sometimes will backfire through the intake on acceleration. No trouble codes stored,TPS seems ok. I hope to get some suggestions as to where to start/common problems etc. Have absolutely zero experience with ZR-1's. Seems to run ok down the road unless you let off the throttle and try to accelerate again,then there is a big hesitation and eventually will accelerate. Car has 27000 miles on it.
Also,on initial start up cold or after sitting for a while,the engine sounds like it is loose/rattling/knocking until oil pressure comes up. Is this common?
Thanks,
Jim B.=VP

90 Corvette ZR-1 · 05-02-2005, 06:05 PM

the chain slap is normal.

8388 · 05-02-2005, 06:12 PM

Sounds like the vac line to the map sensor came off. Sensor is located at the center rear of the plenum.

Z Factor · 05-02-2005, 06:44 PM

Quote:

Originally Posted by 8388

Sounds like the vac line to the map sensor came off. Sensor is located at the center rear of the plenum.

Could be an injector issue as well, but the map sensor line is easy to check and a common problem for those symptoms.

Also as said above, the initial noise is normal.

vette punk · 05-03-2005, 02:35 PM

You hit it on the head with the map line problem,replaced map line and now runs good. Still idles high,the IAC counts are at zero,indicating a vacuum leak or a misadjusted tthrottle plate. Any common concerns to look for as far as the high idle? Do not see any vacuum leaks and the throttle body does not appear to have been tampered with.
Thanks,
Jim B. = VP

90 Corvette ZR-1 · 05-03-2005, 02:38 PM

could be the chip. Is he using the stock chip?

vette punk · 05-05-2005, 06:48 PM

Checked the chip,stock factory PROM.

90 Corvette ZR-1 · 05-05-2005, 08:05 PM

Quote:

Originally Posted by vette punk

Checked the chip,stock factory PROM.

I think we found the problem

vette punk · 05-06-2005, 07:35 PM

Is there a problem with it having the stock PROM or chip?
Jim B.

8388 · 05-06-2005, 07:53 PM

Quote:

Originally Posted by vette punk

Is there a problem with it having the stock PROM or chip?
Jim B.

Nope. But G.M did offer a recalibrated chip for it. The recalibrated chip should correct drivability issues like the one your having.