I'm trying to help my uncle out with his all stock 87 K-5 Blazer with a 350 TBI (I mean third gen ) . The problem is that when the car is warmed up and sitting at a stop, the idle drops down about 100-150 RPM, and then once he tries to move again, the car stalls, cuts off, and has to be restarted. This happens any time at sits at a stop for more than 5 seconds.

Today I decided to check a couple of things. The resistance of the injectors are fine (1.5 ohms) and there aren't any apparent vacuum leaks. I hooked up my scan tool to watch the data as the problem occurs, and I noticed that the engine goes lean and stays lean when it idles down (stays around 150-200 mV). So something is causing the truck to run lean at idle, but the O2 sensor values are fine when cruising (constantly varies anywhere from 150-850 mV). I can't quite remember, but I'm pretty sure the idle air counts stayed around 50 to 100 at idle and cruising.

These are the parts or things that have been replaced by previous mechanics: MAP sensor, IAC valve, TBI mounting gasket, fuel pressure was checked (said it was 13 PSI), vacuum lines checked.

Does anyone have any suggestions or advice? I am going to check all the vacuum lines and fuel pressure soon, just to be sure. My uncle is getting frustrated with this problem. He has to restart it constantly everywhere it goes. Thank you for any help.

P.S. Sorry for such the long post.

 

If it only happens when it's warmed up:

- maybe try checking/replacing the coolant temperature sensor. $8 or less at Napa and 5 minute swap.
- could there be a possible exhaust leak causing 02 readings to read lean?

 

Those are good suggestions, thanks. I'll check both of those things out when I work on again soon.