Hey guys, my name is Jason. I'm from Midland, MI. I have had a 1985 Corvette for about 1 month now. Since I've had the vehicle I have noticed a throttle hesitation when I hit it hard at takeoff. It bogs down for about 1 second then takes off. When I'm driving normally lets say about 50 MPH If I barely push on accelerator I can tell its not running right. Seems to be worse when cold also. Here is a list of whats been done within the first month of ownership.

Fuel Pump
Fuel Filter
Throttle Position Sensor
Idle Air Control Motor
Mass Air Flow Sensor
Plugs & Wires
Air Filter (K & N)
Throttle Body Clean
Timing Set to 6
PCV Valve
Idle set Properly

Also at work we use a SOLUS Scanner and there are no codes or stored codes. I dont know what else to do. The hesitation is still there. Any suggestions would be greatly appreciated. Thank you, Jason

 

Well - I'll throw my two cents worth in... Is the motor "stock"? OEM cam, stock exhaust, etc? Is the PROM the original GM chip or something else?

I know what I would do, on My '85, to correct such a hesitation problem, but what I have is a long way from original, in a lot of different ways, and I have the luxury of editing/burning my own chips.

You didn't say, but I assume you have checked the fuel pressure? Do you have an adjustable regulator on the car - if so raising the pressure a few pounds might help the problem.

I also assume that you must have re-set the TPS voltage at idle when you changed it. Re-setting that position to a few tenths of a volt higher at the idle setting - say .54 volts instead of .50 - might also help cover the hesitation.

You could also play with the PE stuff in the chip and the MAF vs pulse width table to richen the thing up a bit - assuming that it is going lean, which might not be the case.

Actually - if it was really going Rich for a second...how did you check the TPS voltage - with the car running? The reading won't be the same if it's Not running - key on engine Off battery voltage is low, and the Supplied voltage to the TPS won't be the same as it is with the engine actually Running...

You might also try bumping the base timing setting up a couple of degrees - say 8-10 instead of 6, and see what That does. If it's not a "stock" chip the base timing setting in That might not be OEM.

 

A hesitation in throttle response usually indicates a lean condition. You certainly have changed a lot of parts, but on a car this old it was probably warranted.
I would suggest trying another PROM that enriches the mixture?
Also, make sure you do not have a vacuum leak that is being compensated for up by the IAC.

 

complete tune up, rotor dist cap, plug wires, plugs, reset timing, disco batt cable to set ecm to default then drive. if problem remains try to scan and see if IAC is out to far, amybe the butterflies dont close all the way.

 

i agree with everything said. i am chasing hesitation, did all orignal guy said, i am thinking fuel pressure ? also i did up grade ... i thought? computor chip. or tps sensor volts.
i have been looking at this forum since i got my VETTE, this is the first time i signed in. this site is priceless.. garage and pics to follow..
thank you all

 

I may have missed it, bit I didn't read that the oxygen sensor was. changed. I would try this along with plugs and wires.

 

This thread is more than 6 years old. Please start a new thread most likely in discussion and tell us about your car.