97 silverado 5.7 won't idle

97conversion · September 5, 2015

Problem: I have 97 Silverado 5.7 that won't idle.

Heres the story: I bought this in march 2015. It had a slight miss at idle but runs fine otherwise. 155K miles. The check engine light would stay on constantly with a p0300 and p0305 code. Took me a while to figure out I have 110 psi in the number 5 cylinder so looks like I need a valve job.

I've been running the truck as is until I get around to pulling the heads. The other day I was driving the truck and it died at idle. Ever since then it will not idle. I can start it and give it gas to keep it running. It revs up fine but just will not idle once I take my foot off the gas.

It looks like the previous owner had replaced a lot of stuff trying to figure out the original valve problem. It has new wires, plugs, cap, rotor. Fuel spider has been replaced. Looks like the idle control module may have been replaced.

I suspect my fuel pressure is fine as it runs fine if you give it gas. Maybe EGR??? No vacuum leak that I can tell but its hard to figure that out now that it won't idle. But the big question is should I be trying to diagnose this problem knowing I have a burnt valve issue? Should I just get the valve job done then figure this out? I'd really like to have it running so after I do the valves I know it will fire right up with no problems

THanks

1997 Z71 Silverado K1500

Centurion Conversion Crew Cab

5.7l V8

Doug_Scott · September 6, 2015

When you did the compression test did you put some oil into the low compression cylinder? Have you pulled the drivers side valve cover and check that all the rockers are moving roughly the same amount?

You should at least check fuel pressure. I would also pull the IAC motor and clean both the stepper motor and the throttle body where it bolts in. Idle speed is controlled by the IAC stepper motor, and if it has all kinds of crap in the orifice it runs in, idle quality will suffer.

Duelin · September 7, 2015

Could be the EGR valve is carboned up and the pintle is stuck or not seating completely. I would take it off and check it and clean it. It not going to cost you anything. Maybe a gasket.

97conversion · September 7, 2015

I'm pretty sure its a valve and not the rings. Didn't put oil in the cylinder but the way it built pressure was similar to a valve issue.

I had previously cleaned the throttle body when I was going to replace the fuel spider and found out it was brand new. I removed the IAC today and found that thing is new too. Hardly any carbon build up at all, very clean.

I then conducted a some tests on the EGR valve. I used the procedure outlined in the Haynes manual. It is getting 5 volts from the PCM. I then checked for continuity on the valve itself between terminals 2 and 4; and terminals 1 and 5 . The book says, "if either check reveals an open circuit, replace the EGR valve." My test showed continuity between 1 and 5 (indicated by a beep from my digital multimeter).

Is it possible that my EGR is bad and allowing exhaust gas into the intake at idle??? If so, this is likely the reason it will not idle.

rdnkcpa · September 7, 2015

I had a similar problem to yours, but on a 4.3L V6. I was getting a P0300 with the A/C running at idle. I was not getting a cylinder specific misfire. I pulled the engine last winter to put a new oil pan gasket, timing chain cover gasket, intake gaskets, and rear main seal. When I had the engine out I upgraded the fuel injector spider hoping to cure my P0300. I also cleaned up the EGR valve as best I could and reinstalled that. Other than the P0300 that just shows up when the A/C is on truck ran good. Last weekend I decided to chase the P0300 again. Did some google research and the first thing I did was check for vacuum leaks. Good to go, none that i could find with a can of carb cleaner. Replaced the EGR valve, light instantly cleared but came back an hour later after letting it idle with A/C on for 15-20 minutes. Since it was at idle, and the truck has 200K on it I put in a new idle air control valve, 3 new O2 sensors (S10 4.3 only has 3), new PCV valve and hose. New O2 sensors, EGR and IAC has cured my problem. The truck starts easier, shifts smoother, and runs much better overall. The CEL light went out, I have driven the truck in some pretty nasty rush hour traffic with A/C blowing full blast. So far so good!! Interweb research also pointed to having a worn distributor, where the top bearing wears out and causes the rotor to wobble up and down. That is an easy check, pull the distributor cap and see if you can move the rotor up and down. The fuel pump quit on me this spring, so that was replaced as well. That was the second time I replaced the fuel pump. When I had the engine out last winter I replaced all plugs, wires, cap, rotor, and I put a new ignition coil in as well. Those were all maintenance items, and needed to be done anyway.

I know some people on this board will blow a gasket over throwing parts at it, but new AC-Delco O2 sensors were $23.11 each, new AC-Delco IAC was $66.00, and new AC-Delco EGR was $116.00, PCV was $4.88, and hose was $9.00. I have $256.00 in parts in it(from last weekend), still probably cheaper than having a shop fix it. The truck has 215K miles on it, and everything that I replaced (last weekend) was factory original, so I'm chalking these parts up to maintenance items. You can go even cheaper on the parts and buy Standard Motor Products. I did buy the SMP fuel spider last winter and so far that has worked out well. I also pulled the MAF sensor and sprayed it down with MAF sensor cleaner and reinstalled that.

The only thing that I really wanted to do when I had the motor out last winter that I did not do was have it rebuilt, but funds were tight. It ran well, did not knock, and burned a quart of oil for every 4-5K miles, so I could not justify the $$ on having it rebuilt.

97conversion · September 17, 2015

New EGR valve did not work. I'm blaming Haynes on that one.

Finally got around to doing the fuel pressure test. I have about 55psi when I turn the key on. The Haynes Manuel and other online sources say 60-66psi is what it should be. Again, it will start if I give it some gas and will only run while giving it gas. I did the leak down test and it appears the regulator and injectors are fine. The regulator is attached to that fuel spider under the plastic plenum and not easy to get to. Also, most of those fuel spiders come with a new regulator on it and I know mine is new.

Therefore, looks like I'm going to replace the fuel pump. (I already replaced the fuel filter so I know that is not clogged). From the looks of online articles it looks like many times when fuel pumps go bad they still work, they just don't put out the required pressure. Probably going to remove the bed as I have 3/4 of a tank of gas.....We'll see.