94 454, GMC Suburban -Idle Air Control, O2, TPS, Fuel Pump relay all replaced-still code 12, 36

jamesT · Jul 31, 2022

I sprayed the EGR with the throttle body cleaner. Pushed the valve in with the straw, then blasted inside with the valve depressed in - while holding the unit upside down. The valve play improved dramatically. Cleaned the throttle body. Put valve back.

Started engine, no light, better running.

Going to replace fuel filter and add a can of seafoam with fill of gas and let er rip, see how she goes.

Thanks everyone, will report back shortly.

jamesT · Aug 11, 2022

Replaced EGR yesterday. Truck ran better, I guess? Light was off. Went on again couple hours later. Then went off again next time truck was started. Going to have to do a throttle body rebuild.

Not always, but the throttle still sticks and jumps when I press the pedal to accelerate.

PlayingWithTBI · Aug 11, 2022

jamesT said:
Not always, but the throttle still sticks and jumps when I press the pedal to accelerate.

Has someone been playing with the minimum idle screw located behind the little plug? I had my throttle stick when accelerating from idle, it turned out the cable was sticking on the sleeve that goes over it at the Throttle Body. I wound up screwing the min stop in ~1/2 turn and got it smoothed out. YMMV

udidwht · Aug 11, 2022

Be sure you get the correctly sized IAC. There are (2) different pintle sizes.

jamesT · Aug 31, 2022

So, added seafoam, changed fuel filter, also filled tank and added octane boost.

It runs like it would rather be a Tesla.

Taking it to an old school pro-rare in these parts to give it a throrough looking over.

Another old timer told me that these engines were prone to intake manifold leaks as well as base of the throttle body gasket leaks. He said to spray a bit of water from a spray bottle at these gasket areas, if the motor changes how it runs, the gasket is your culprit.

jamesT · Aug 31, 2022

termite said:
www.gmt400.com/threads/95-k2500-suburban-454-ses-code-36.55915/

Post 10 has the P/N for the culprit of my code 36 issue. Vacuum ports were reversed from original.

Great read, thanks for the direction. Still chasing the problem.

jamesT · Aug 31, 2022

udidwht said:
Be sure you get the correctly sized IAC. There are (2) different pintle sizes.

Checked pintle size, confused the parts counter people.

Appears they did not know as the specs did not indicate. I appear to have the right one. I'll have to re-check to make sure. Thank you.

jamesT · Aug 31, 2022

Schurkey said:
The foam is a "filter" that the new item should have also.

Maybe there's some internal filter...

If the gas pedal is sticky, it may not close properly, leading to high idle. A worn throttle body can cause this. Repair is to remove the throttle plates, throttle shaft, TPS, etc., and re-bush the throttle body.

Connect a scan tool, look at the IAC movement and TPS.

This to me, sounds like the most plausible explanation for the suction feeling. As far as scan tool. Hard to come by in these parts. Many garages who used work on and safety inspect these vehicles have relinquished their small vehicle inspection licences and gotten rid of old diagnostic tools and have take the same line as the dealerships and will not touch a vehicle older than 10 years.

udidwht · Aug 31, 2022

94 have an electric operated EGR.

evilunclegrimace · Aug 31, 2022

Unhook the throttle cable from the TBI linkage and see if the idle returns to normal. I have had to replace the throttle cable on several of my trucks. The metal cable eventually wears in to the sheath material causing the cable to stick resulting in high idle and/or higher than normal effort to depress the throttle pedal.

94 454, GMC Suburban -Idle Air Control, O2, TPS, Fuel Pump relay all replaced-still code 12, 36

jamesT

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jamesT

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PlayingWithTBI

2022 Truck of the Year

udidwht

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jamesT

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jamesT

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jamesT

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jamesT

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udidwht

I'm Awesome

evilunclegrimace

Does not always play well with others

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