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B1rdman · 02-25-2011, 06:05 PM

I have a 1987 Chevy Silverado, 350 or 5.7 engine with TBI. I have had the truck for 17 years and it has about 171 k miles on it

Cold it starts up and runs fine. It even runs fine when warm except when you come to a stop sign or light and have to sit at it for more that 10 seconds where it dies. It will die also when you put it in reverse and turn the steering wheel while at idle. It seems to be like a low idle issue. It starts right back up with no problems and if you can catch it by putting it into neutral or keeping one foot on the brake and giving it a little gas it does not die when coming to a stop.

I actually have had this problem with the truck for several years but its dying has gotten a little more frequent of late so I am trying to find out for once and all what is the matter. Even with the miles it has been a very good truck.

I have actually taken it in to a couple of very good shops over the years for them to put it on the scanner and other test equipment and they could not find any problem.

There has been no codes at any time on it.

Using the diag mode with the key on I watched the IAC relearn process through the top of the throttle body.

I Changed the MAP out with a known good one.

The egr seem properly seated with no leaks, there is no rough or high idle

Checked the CTS with millimeter for resistance at high and low temp. 70 degree it showed 3900 ohms and at 210 it was right at 200 ohms.

Checked for vacuum leaks with carb/TBI cleaner around the base of TBI. Checked all vacuum lines

Injectors are not leaking and have a nice conical patterns.

Sensor voltage is right at 4.9 volts. The standard is 5 volts plus or minus .5 volt. I cleaned and tested sensor grounds.

The truck just made a 2000 mile trip from Wa state to Texas with a load in back and had no problems except the occasional dying issue when leaving the interstate. Throttle never felt starved and could maintain 70 mph easy with a lot of throttle response. So I do not think this is a low fuel pressure issue.

The only thing I have not been able to do it check the timing since I do not own a light. I have a friend who has one who is coming over this weekend with it so we can see if it might have a timing or distributor issue. He thinks it’s a wore out distributor. So with the computer disconnected if it shows 0 degrees TDC and a steady timing mark, I do not think it’s the distributor actually causing it to die. Normally a wore out distributor causes a rough idle unless the module itself might be causing a low idle.

The only things left I have not checked because I can not afford to throw parts at it is the distributor, TBI, Computer. I thought the TCC might be causing it, but I was able to get it to die just sitting in my driveway after getting it to operating temp, by putting it into gear and turning the steering wheel while at idle.

Since I do have a way to monitor the rpm I have not done the minimum air adjust. Since it is actually running good except for the idle issue I do not want to mess with something that might make it less drive able right now.

I guess I am looking for anything that I might have missed here that will not cost me an arm or leg to test it or some other indications that I might be missing.

02-25-2011, 06:05 PM	#1
B1rdman Registered User Join Date: Feb 2011 Location: Amarillo, Texas Posts: 3	87 Chevy 350 TBI low Idle issue I have a 1987 Chevy Silverado, 350 or 5.7 engine with TBI. I have had the truck for 17 years and it has about 171 k miles on it Cold it starts up and runs fine. It even runs fine when warm except when you come to a stop sign or light and have to sit at it for more that 10 seconds where it dies. It will die also when you put it in reverse and turn the steering wheel while at idle. It seems to be like a low idle issue. It starts right back up with no problems and if you can catch it by putting it into neutral or keeping one foot on the brake and giving it a little gas it does not die when coming to a stop. I actually have had this problem with the truck for several years but its dying has gotten a little more frequent of late so I am trying to find out for once and all what is the matter. Even with the miles it has been a very good truck. I have actually taken it in to a couple of very good shops over the years for them to put it on the scanner and other test equipment and they could not find any problem. There has been no codes at any time on it. Using the diag mode with the key on I watched the IAC relearn process through the top of the throttle body. I Changed the MAP out with a known good one. The egr seem properly seated with no leaks, there is no rough or high idle Checked the CTS with millimeter for resistance at high and low temp. 70 degree it showed 3900 ohms and at 210 it was right at 200 ohms. Checked for vacuum leaks with carb/TBI cleaner around the base of TBI. Checked all vacuum lines Injectors are not leaking and have a nice conical patterns. Sensor voltage is right at 4.9 volts. The standard is 5 volts plus or minus .5 volt. I cleaned and tested sensor grounds. The truck just made a 2000 mile trip from Wa state to Texas with a load in back and had no problems except the occasional dying issue when leaving the interstate. Throttle never felt starved and could maintain 70 mph easy with a lot of throttle response. So I do not think this is a low fuel pressure issue. The only thing I have not been able to do it check the timing since I do not own a light. I have a friend who has one who is coming over this weekend with it so we can see if it might have a timing or distributor issue. He thinks it’s a wore out distributor. So with the computer disconnected if it shows 0 degrees TDC and a steady timing mark, I do not think it’s the distributor actually causing it to die. Normally a wore out distributor causes a rough idle unless the module itself might be causing a low idle. The only things left I have not checked because I can not afford to throw parts at it is the distributor, TBI, Computer. I thought the TCC might be causing it, but I was able to get it to die just sitting in my driveway after getting it to operating temp, by putting it into gear and turning the steering wheel while at idle. Since I do have a way to monitor the rpm I have not done the minimum air adjust. Since it is actually running good except for the idle issue I do not want to mess with something that might make it less drive able right now. I guess I am looking for anything that I might have missed here that will not cost me an arm or leg to test it or some other indications that I might be missing.