Infrequent RPM drop to 200 and stall

[DmitryGMT800]

Greetings. I would like to ask your opinion on the issue with my 2002 Tahoe. Sometimes there is severe drop in RPM after I start engine - idle drops to 300/200 rpm. When I try to shift to Drive it may drop to 200 or even 100 rpm and stall. It is possible to rev the engine and drive, during which transmission bumps can be felt. It is enough to start engine a couple of times to overcome this problem and vehicle would drive well for several months. The issue does not seem to depend on cold or hot engine, weather, fuel, its level etc.
I tend to think of erratic work of throttle position sensor, or some other sensor responsible for air.

 

[Fless]

Being a 2002 I assume that this is a drive by cable (DBC) throttle body? The IAC on the throttle body is responsible for control of idle speed. Clean the TB.

You may also need to look for a vacuum leak. What do your fuel trims look like at idle?

 

[DmitryGMT800]

Yes, it is DBC version throttle body. I have cleaned it about a year ago, but will do that again. I am also looking forward to replacing the idle air sensor as well. Will try to check the trim data through Torque app via OBD. Sometimes vehicle does not start at first crank - when I repeat a loud thud is heard from the exhaust manifold... I was told it may be the fuel pressure sensor failure.. may this sensor cause RPM fluctuations? I am ordering the part GM GENUINE 2173073

 

[DmitryGMT800]

Here are some screens from diagnostic application. Normal idle after morning start, outside temp 24C degrees. Could not recreate faulty behavior. STFT1 fluctuates mostly within 0.8%-3.9%

 

[rockola1971]

Being a 2002 I assume that this is a drive by cable (DBC) throttle body? The IAC on the throttle body is responsible for control of idle speed. Clean the TB.

You may also need to look for a vacuum leak. What do your fuel trims look like at idle?

Yep id completely pull the throttle body and clean it with brake cleaner. The IAC has to come out and clean the part and the ports in the throttle body with brake cleaner.

 

[DmitryGMT800]

Yep id completely pull the throttle body and clean it with brake cleaner. The IAC has to come out and clean the part and the ports in the throttle body with brake cleaner.

I have done the complete cleaning of the throttle body with a specialized cleaner 2 years ago and changed the gasket. I am looking forward to clean it again along with the MAF sensor.

 

[DmitryGMT800]

Update: Changed spark plugs and Fuel pressure regulator 4 days ago - engine starts instantly and works smooth so far. Will change fuel filter later this month.
I consider the issue to be solved. Thank you for assistance.