5.3 Rough Idle - But No Ecu Code

I have 2000 Tahoe with 5.3 with 63k miles on it. For last 1,000 miles the engine idles rough when warmed up with tranny in drive. BUT NO "CHECK ENGINE" CODE IS TRIGGERED. Twice in last 2 weeks I have had injectors cleaned (at 2 different shops...on a Chevy dealer). The throttle position sensor (TPS) checks out OK. The Idle Air Control Valve above it also checks out OK. The fuel pump was also replaced because of unstable fuel pressure. The rough idle is better now...but NOT totally smooth like it used to be. ??? Again...NO ENGINE CODES TRIGGERED. Any suggestions?

Try disconnecting the vaccuum hose to the top of the fuel pressure regulator , turn the key on two or three times to see fuel spurting out of regulator that has a busted diaphragm. If you pull the line off and it is wet,just replace regulator. I've replaced 4 in last 6 months.2 different designs available, most are what is called "side outlet" where nipple is actually facing straifgt up toward hood. Hope this helps. No codes were ever stored for this problem.

Just curious wild Bill. Why would you replace a 4 diaphrams in six months. Are you using aftermarket parts ???

It was 4 separate vehicles I have fixed and I only use gm regulators.Have you had any luck with yours?

Thanks for the reply WildBill. Oh, 4- different vehicles, that makes more sense, guess it was the way it was written. Reading some of your other inserts, seems your on top of things. Enjoy reading your replys, you sound knowlegeble in some aspects of areas.

Thanks. I have the opportuninity every day to work for a great boss who takes in just about everything that has an internal combustion engine. Audis to Zephyrs and everything in between. We crave info. We even have a Delorean at the shop and have had a 1953 Sunbeam Talbot Convertible in for work.

Hey Wild Bill,

I have a 98 Tahoe with what I believe is fuel delivery problems. It's been stalling when shifting out of drive into reverse or park when the A/C is on.

I've tried replacing the TPS and IAC.

I've replaced the Fuel Pump assy three weeks ago because the original pump (138k mi) was screaming. The new pump was quiet for a couple days and now it's almost as loud as the other one.

Yesterday it has gotten worse where I cannot push the accelarator down more than half way. If I do, it doesn't go above 3500 RPM and the VCM spits out codes P0131 and P0151, which is the saying the O2 sensors are really lean for a long period of time.

Lucky I have a Snap-On code scanner this weekend from a buddies shop to help me troubleshoot this problem.

I have put a fuel pressure gauge on the test port and I need to know if this sounds normal:

Key On, Engine Off, 60 PSI
Key On, Engine Idle, 50 PSI
Key On, Accelerating, 52 to 62 PSI coinciding with throttle

Books say 60-66 PSI for this Vortec motor at 0 RPM, but is 50 PSI too low?

How hard is to get to the fuel pressure regulator inside that intake?

thanks!

Jay

UPDATE:

I was able to test the fuel pressure on a 96 Vortec Motor today in a different Tahoe and I got the same results on the gauge. His stayed around 58 PSI with key on, motor off and down to 50 PSI when engine was idling.

So, I decided to replace the Fram fuel filter today with one from Napa and the pump stopped squealing as loud as it was. My throttle response has come back when over 3500 RPM but now my idle is really high so I'm going to reset the computer for an hour or so and go back out later and check it.

I wonder if the Fram filter was causing the stall problem also? I replaced it about 6 months ago and I was very surprized it was clogged or bad.
I think I had the stalling problem the end of last summer but when I stopped using the A/C in the winter I forgot about it.