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B1rdman · 02-26-2011, 10:19 AM

Here let me answer a couple of questions.

I did not check the voltage on the TPS on this round of troubleshooting but I did a while back and so did the shops I took the truck to to see if a scanner would find anything. Supposedly the voltage then was nominal and correct and the TPS show smooth operation from idle to WOT. I will test the voltage again when I check my timing and distributor later.

I used the reference voltage on the MAP sensor to check the source voltage for the sensors as applied from the regulator circuit on the computer. It showed within specs as listed.

My initial thoughts and on more than one occasion that this was an IAC problem. However I pulled the IAC and the Pintel was not gummed up but I sprayed cleaner into the area in which the pintel goes. I did not spray any cleaner into the IAC. I checked to make sure that the pintel was exactly 1 and 1/8th of an inch out and reinstalled it. I jumpered and pins A and B in the diag connector and got on top of the engine to observe the IAC relearn process through the top of the TBI while I had a helper turn the ignition switch to on w/o starting it. I observed proper mechanical operation during the relearn process. According to everything I have read about the IAC, this is an indication that it works properly both mechanically and electrically. If it is an IAC problem then its the controller to the IAC which is the computer, IMHO.

When cold the engine runs at a slightly higher speed and slows down as it gets warm. It seems normal when in park and does not run rough anytime at idle or at speed. It makes me think it does not get the boost in idle by a 100 or so rpm when in gear. I have not tried the AC to see if it kicks the rpm up. Living in the Pacific Northwest I have not had to use my AC in a long time. I will have to check that out also.

If the temperature is above about 40 degrees, all I have to do to start the truck is turn the ignition on and wait a few seconds(5 or 6) for the fuel pump to charge the system then without touching the throttle, the trucks starts right up. If its colder than 40 then it depends how much colder on how much throttle I have to give to get it started. Around zero I have to work the throttle a little to get it started and keep it running for the first few seconds. But it has always started this way since I bought the truck. I have never had a problem starting it. In fact it has been the easiest starting vehicle I have ever owned.

I will get back when I double check all of these things later when I get the timing light to check the timing.

02-26-2011, 10:19 AM	#4
B1rdman Registered User Join Date: Feb 2011 Location: Amarillo, Texas Posts: 3	Re: 87 Chevy 350 TBI low Idle issue Here let me answer a couple of questions. I did not check the voltage on the TPS on this round of troubleshooting but I did a while back and so did the shops I took the truck to to see if a scanner would find anything. Supposedly the voltage then was nominal and correct and the TPS show smooth operation from idle to WOT. I will test the voltage again when I check my timing and distributor later. I used the reference voltage on the MAP sensor to check the source voltage for the sensors as applied from the regulator circuit on the computer. It showed within specs as listed. My initial thoughts and on more than one occasion that this was an IAC problem. However I pulled the IAC and the Pintel was not gummed up but I sprayed cleaner into the area in which the pintel goes. I did not spray any cleaner into the IAC. I checked to make sure that the pintel was exactly 1 and 1/8th of an inch out and reinstalled it. I jumpered and pins A and B in the diag connector and got on top of the engine to observe the IAC relearn process through the top of the TBI while I had a helper turn the ignition switch to on w/o starting it. I observed proper mechanical operation during the relearn process. According to everything I have read about the IAC, this is an indication that it works properly both mechanically and electrically. If it is an IAC problem then its the controller to the IAC which is the computer, IMHO. When cold the engine runs at a slightly higher speed and slows down as it gets warm. It seems normal when in park and does not run rough anytime at idle or at speed. It makes me think it does not get the boost in idle by a 100 or so rpm when in gear. I have not tried the AC to see if it kicks the rpm up. Living in the Pacific Northwest I have not had to use my AC in a long time. I will have to check that out also. If the temperature is above about 40 degrees, all I have to do to start the truck is turn the ignition on and wait a few seconds(5 or 6) for the fuel pump to charge the system then without touching the throttle, the trucks starts right up. If its colder than 40 then it depends how much colder on how much throttle I have to give to get it started. Around zero I have to work the throttle a little to get it started and keep it running for the first few seconds. But it has always started this way since I bought the truck. I have never had a problem starting it. In fact it has been the easiest starting vehicle I have ever owned. I will get back when I double check all of these things later when I get the timing light to check the timing.