HIGH idle - ZR-1 Net Registry Forums

ddiblasio · 12-13-2023

My 94 Z suddenly began to have a high idle in the early summer. 1800 rpm cold, 1600warm. Electronic Vac pump (which is new) wont shut off. I followed the vacuum leak articles my Marc Haik. removed plenum, removed all hoses (I think) checked for breaks in the lines etc replace vac cannister, IAC, etc etc.
followed Marcs Plenum video replacement to the T.
I removed Plenum and did this 3 times( all new gasket kits from Jerrys Gaskits.
If i remove the main vac line coming off the elec vac pump and put my finger over the hose it shuts off.
I invested in a smoke generator and hooked it to the vac line to the break booster pump. saw a minimal amount of smoke coming from the throttle body butterfly plates but not much.
AC stopped working the same time this idle issue happened.
What have I missed??
if you could call me Dennis DiBlasio 609 685 3661, and I can give you many more details. Thank you!

1991 Corvette ZR-1 · 12-14-2023

Off the top of my head, it may be a TPS adjustment issue. Even with an air leak of reasonable size, at its normal idle position, I wouldn?t think there?s enough fuel present intended for 650 to 750 rpm that could more than double the idle speed if enough air was present.

The TPS would be responsible for talking to the ECU which could then respond with the fuel pulses to match the interpretated air flow based on TPS position. I believe the voltage reading at idle should be .54 volts, without having a manual in front of me at the moment.

The AC not working during the same time may be related to a specific condition built into the system operation. Possibly due to the high idle speed in which the ECU sends a signal to the AC clutch to disengage because the vehicle is stationary and not moving.

ddiblasio · 12-15-2023

I appreciate your insight and input and will check into this.
I also replaced my twin pumps for a single hi psi fuel pump as per Marc H.
But the fact the electronic vac pump running full time seems to indicate a leak somewhere.

12-13-2023	#1
ddiblasio Join Date: Jul 2023 Location: Moseley VA Posts: 5	HIGH idle My 94 Z suddenly began to have a high idle in the early summer. 1800 rpm cold, 1600warm. Electronic Vac pump (which is new) wont shut off. I followed the vacuum leak articles my Marc Haik. removed plenum, removed all hoses (I think) checked for breaks in the lines etc replace vac cannister, IAC, etc etc. followed Marcs Plenum video replacement to the T. I removed Plenum and did this 3 times( all new gasket kits from Jerrys Gaskits. If i remove the main vac line coming off the elec vac pump and put my finger over the hose it shuts off. I invested in a smoke generator and hooked it to the vac line to the break booster pump. saw a minimal amount of smoke coming from the throttle body butterfly plates but not much. AC stopped working the same time this idle issue happened. What have I missed?? if you could call me Dennis DiBlasio 609 685 3661, and I can give you many more details. Thank you!

12-14-2023	#2
1991 Corvette ZR-1 Join Date: Sep 2018 Location: Florida Posts: 294	Re: HIGH idle Off the top of my head, it may be a TPS adjustment issue. Even with an air leak of reasonable size, at its normal idle position, I wouldn?t think there?s enough fuel present intended for 650 to 750 rpm that could more than double the idle speed if enough air was present. The TPS would be responsible for talking to the ECU which could then respond with the fuel pulses to match the interpretated air flow based on TPS position. I believe the voltage reading at idle should be .54 volts, without having a manual in front of me at the moment. The AC not working during the same time may be related to a specific condition built into the system operation. Possibly due to the high idle speed in which the ECU sends a signal to the AC clutch to disengage because the vehicle is stationary and not moving. Last edited by 1991 Corvette ZR-1; 12-14-2023 at 08:22 PM.

12-15-2023	#3
ddiblasio Join Date: Jul 2023 Location: Moseley VA Posts: 5	Re: HIGH idle I appreciate your insight and input and will check into this. I also replaced my twin pumps for a single hi psi fuel pump as per Marc H. But the fact the electronic vac pump running full time seems to indicate a leak somewhere.