94 5.7 TBI Power steering causing stalling?

[Woodwright]

I have a 94 GMC K1500 and having an issue only when the engine is warm. After driving around, parking and coming back to the truck and backing out of a spot, whenever the steering wheel is turned the engine RPMs drop and the truck stalls. Turn left or right it stalls. Forward or reverse, does the same thing. Have to give it some gas to keep the RPMs up and not stall.

Prior to this, I was getting a code 32. Checked the EGR valve and it had a bad diaphragm. Swapped it out with AC Delco 214-5073 and cleared the code--all is well. But the truck still stalls at idle with the engine is warm and the wheel is turned.

Could power steering cause this?

 

[rzr6-4]

The "power" from your power steering comes from the belt bieng spun by the crank. AC, alternator, water pump, power steering all introduce their own drag on the system. If your engine is already struggling to run, yes your power steering will bog it down even more when you try to turn.

It sounds very similar to what mine does. Runs rough just above idle and when I'm shuffling around parking lots, right in that problem RPM range, I can actually feel my power steering come and go as the RPMs surge, fighting the urge to stall. I suspect I need to change my EGR like you did.

 

[Woodwright]

The "power" from your power steering comes from the belt bieng spun by the crank. AC, alternator, water pump, power steering all introduce their own drag on the system. If your engine is already struggling to run, yes your power steering will bog it down even more when you try to turn.

It sounds very similar to what mine does. Runs rough just above idle and when I'm shuffling around parking lots, right in that problem RPM range, I can actually feel my power steering come and go as the RPMs surge, fighting the urge to stall. I suspect I need to change my EGR like you did.

Thanks, ran it around a few times with and without the A/C running. Stalls only with A/C on. Suspect the TPS...

 

[PlayingWithTBI]

Stalls only with A/C on. Suspect the TPS...

Normally, the PCM sees you turned on the A/C and increases counts to the IAC to compensate for the added draw. It will also adjust when you turn the wheel. Your AIC may not be opening or responding enough. With a scanner, you'll see IAC Steps Commanded but, not its actual position (it's a 4 wire stepper motor with no feedback). You may get lucky if you reset it and check your Min Idle RPMs. It's not suggested to mess with that screw behind the cover in front but, someone may have to so you don't lose too much before the PCM/IAC can respond.

Here's a .pdf with the instructions for resetting your IAC, Min Idle Screw, and TPS. I'd do this before throwing any parts at it.

 

[GoToGuy]

Second that motion, check IAC, the ECM and it play together.

 

[JDGMC]

What are the rpm’s in P and D w/AC off and on @ operating temp?

 

[1998_K1500_Sub]

Normally, the PCM sees you turned on the A/C and increases counts to the IAC to compensate for the added draw. It will also adjust when you turn the wheel. Your AIC may not be opening or responding enough. With a scanner, you'll see IAC Steps Commanded but, not its actual position (it's a 4 wire stepper motor with no feedback).

^^^ This.

It would be useful to know the IAC position being commanded by the ECU when the engine's idling and warm (which is when OP's problem can occur).

If the IAC is being commanded to almost maximum (what is it, 127 or 255?), then...

- it can't open any further to maintain the idle under PS load, and

- it shouldn't be that high to begin with, meaning, there's another issue somewhere causing the ECU to command IAC to be open so widely. A bad or sticky IAC valve might cause this, or perhaps another issue.

In fact, the factory service manual has a spec (somewhere) for what the IAC counts ought to be under certain operating conditions (e.g., engine warm, idle, no load). If OP's counts are markedly different, it's again indicative of a potential issue.

I wouldn't mess with the min idle screw unless it was absolutely necessary (meaning... no other cause for the issue could be identified); the min idle should be fine from the factory... in a perfect world, anyway. I realize this adjustment is sometimes necessary when marked changes are made, e.g., a TBI from one engine is grafted onto a different engine, etc.

 

[Woodwright]

Here's a .pdf with the instructions for resetting your IAC, Min Idle Screw, and TPS. I'd do this before throwing any parts at it.

Thanks for sharing that PDF. I'll have to get my hands on a scanner for this.

 

[PlayingWithTBI]

If the IAC is being commanded to almost maximum (what is it, 127 or 255?), then...

IIRC "Park" position (when key is turned off) it goes to ~114. Idle when hot with no accessories ~10 - 40, max ~145. You can go into the .bin and adjust those but, that's a different story (as a example I have mine set @ max 255 for more air flow at WOT).

Another way to adjust the IAC at Idle when hot, is using a scanner to see where it is and adjust the Min Idle Screw where you want. Actually, this is a more accurate way to do it. The procedure in the .pdf I posted can be done simply with a Tach, and the TPS with a DVM.

Note: if it's commanding 0 at idle you run the risk of burning up the stepper motor.

 

[Woodwright]

I pulled the IAC and removed the pintel to clean the carbon buildup from it and the spring. It didn’t seem excessive. Cleaned out the throttle body port as well. Reinstalled and did the IAC reset procedure in the PDF. I’m not going to adjust the minimum idle screw, just not in my comfort zone to make that kind of adjustment given the warnings and my limited skill set here.

Result seem only slightly better. The only time I get it to stall now is when the steering is FULLY turned to the right or left, rather than just beginning to turn the wheel. RPM’s still sound/feel lower than what they should be however. Not sure what they are without a tach or scanner.