91 Camaro Rough Idle (No Codes)

The Car:

1991 Camaro RS 305 TBI (vin 1G1FP23E6ML113392)

The History:

This is my brother’s car he has not even had it for a complete year yet. Last December he bought it for this 16th birthday. It ran but not very well, it had been sitting for the past 3 years and nothing was known about before that. The guy he got it from said he needed money but from the shape the car is in, he didn’t want it anymore. For the past year it has been worked on slowly getting ready to drive. When it went in for inspection on the way home it starting smoking and stalling then shut off. At the time it had a leaking the heater core and the coolant return from the heater core to the radiator. Since then both have been fixed and there seams to be no problem with the cooling system. Only exceptions could possible be a bad sensor. After the engine problem is when I got involved I was asked to swap the motor out. The new motor is a 305 block but came out of a Caprice (this wasn’t know until after the motor was installed). There was an electrical fire that burnt the harness from the headlights and horn to the wiper motor. This was caused from a short in the power supply to the subwoofer amplifier. The harness and amplifier power supply have both been fixed.

The Problem:

The new motor idle good after you start it. Once it has been driven and put into park it starts to idle high while changing the speed. It will go from a high idle to low idle to almost stalling then back to the high idle.

Additional Information:

With the new motor came new wires, cap, and rotor, along with a new thermostat, and O2 sensor. The plugs that are currently there are Bosch, don’t worry they are coming out. The timing has been set to 0 with the ECU unplugged. It was running a high idle at the start until the timing was set. Now it has a low idle until it is driven then jumps up when placed in park.



I am almost sure that the problem is an electrical problem. I am thinking something in the lines of the TPS, MAP, ERG (not so much), or IAC sensors. Unfortunately I don’t have a Hynes manual so any help would be helpful.

Thanks

The Car:

1991 Camaro RS 305 TBI (vin 1G1FP23E6ML113392)

The History:

This is my brother’s car he has not even had it for a complete year yet. Last December he bought it for this 16th birthday. It ran but not very well, it had been sitting for the past 3 years and nothing was known about before that. The guy he got it from said he needed money but from the shape the car is in, he didn’t want it anymore. For the past year it has been worked on slowly getting ready to drive. When it went in for inspection on the way home it starting smoking and stalling then shut off. At the time it had a leaking the heater core and the coolant return from the heater core to the radiator. Since then both have been fixed and there seams to be no problem with the cooling system. Only exceptions could possible be a bad sensor. After the engine problem is when I got involved I was asked to swap the motor out. The new motor is a 305 block but came out of a Caprice (this wasn’t know until after the motor was installed). There was an electrical fire that burnt the harness from the headlights and horn to the wiper motor. This was caused from a short in the power supply to the subwoofer amplifier. The harness and amplifier power supply have both been fixed.

The Problem:

The new motor idle good after you start it. Once it has been driven and put into park it starts to idle high while changing the speed. It will go from a high idle to low idle to almost stalling then back to the high idle.

Additional Information:

With the new motor came new wires, cap, and rotor, along with a new thermostat, and O2 sensor. The plugs that are currently there are Bosch, don’t worry they are coming out. The timing has been set to 0 with the ECU unplugged. It was running a high idle at the start until the timing was set. Now it has a low idle until it is driven then jumps up when placed in park.



I am almost sure that the problem is an electrical problem. I am thinking something in the lines of the TPS, MAP, ERG (not so much), or IAC sensors. Unfortunately I don’t have a Hynes manual so any help would be helpful.

Thanks

well the best chance you would have is to check the EGR or the mass air flow sensor

Thanks for the suggestion. I did end up solving the problem. The bracket on the new carb was bent. I replased it with the original off of the old carb and the car idled right down. Now I am just having trouble with the shifting. It doesn't want to shift right. Takes forever to shift out of first and doesn't stay in second for more then a few seconds.

that sounds like long term abuse from the last owner who couldnt handle the V-8 and the clutch in the auto trans is gone causeing the trans to slip and not shift into higher gears and im guessing the trans is a 700r4 if you deside to replace it put a th350 trans they last forever and give good acceleration and performance