1988 Chevy trouble

okierob · Oct 25, 2011

Need some direction on where to look.

As the subject says. It is a 1988 chevy 1500, 5.7 automatic with throttle body injection.

The problem is at slow speed it will blubber,shudder. Once it gest a little more throttle it will level out and run pretty decent.

If you are just sitting still, it will idle, just when you try to ease into the throttle it will buck,snort and run crappy. Get it out on the road and it will run pretty good at highway speed.

I have replaced the coolant temp sensor as the old one was not reading the right ohms at temperature.

Really would like to figure this out, any help would be appreciated.

Bob · Oct 25, 2011

Disconnect the vacuum tube from the EGR valve and plug the TUBE side. Drive it. LIKELY, it will drive better, but set an EGR trouble code after a few miles.

If it DOES drive better/OK, likely it is time to replace the EGR valve.

tlak · Oct 26, 2011

Symptoms of bad throttle body base gasket

Allan in NE · Oct 26, 2011

Pull a battery cable for a short time to clear all the codes stored.

Drive the truck until the check engine light comes on.

Read the codes and go after the smallest code first. Like Bob says, you're probably gonna see a code 32 pop up.

Tlak suggests a base gasket. Really don't think so because when that joker fails, the idle speed almost always goes way up, as the engine has a vacumm leak. ECM starts dumping extra fuel to compensate/keep the fuel ratio right, which results in a high curb idle.

Oh, and hope beyond hope that the check engine light isn't burnt out. If ya don't have a bulb puller, that cluster has to come clear down to the printed circuit board to change the bulb.

Yeah, I know. I'm rambling this morning............ :>)

Allan

MarkB_MI · Oct 26, 2011

The problem you describe sounds like bad plug wires. Replace the plug wires, distributor cap and rotor and see if that helps. Make sure all the looms for the plug wires are in place.

A short list of other problems I had with my '88:

Bad throttle body gasket (symptom: very fast idle)
Broken lead on distributor pickup coil (symptom: random stalling)
Bad fuel pump
Clogged fuel filter

MarkB_MI · Oct 26, 2011

I could be mistaken, but I don't think the '88 5.7 has EGR. Air pump, yes, but not EGR.

tlak · Oct 26, 2011

To clear codes on a Chevy you pull a cable then touch the positive and negative cables together.
Another culprit can be an O2 sensor.
A fast idle is to over come a vacuum leak and a vehicle isn't going to do that by it's self, it'll stumble at idle and you give it gas to over come it. (some computers may try to over come)

Eugene Alt · Oct 26, 2011

I also vote on oxygen sensor

Bob · Oct 26, 2011

The 1988 K1500 sitting in my driveway DOES have EGR but NO air pump.

Allan in NE · Oct 26, 2011

Not arguein' with ya, just vistin' this morning.

Once you power that ECM down, all codes are lost; I don't care if ya touch the tailpipe to the left front headlight or anything else in between. :>)

Not once does he mention a fast idle. You can hear a bad throttle base gasket from a block away. AND, the fuel trim damn sure WILL overcome the lean condition. That's what it is on there for.

Bottom line tho, instead of just 'guessing' and throwing parts/money at it, get the codes and find the original culprit to start with.

Off to get more coffee. :>)

Allan

Allan in NE · Oct 26, 2011

EGR lives behind the throttle body center right; air pump or no air pump.

It's that big honker right up there close to the EGR solenoid. :>)

Allan

buickanddeere · Oct 26, 2011

As previously stated. EGR leak and/or vacuum leak from emissions lines or gaskets.

VADAVE · Oct 26, 2011

What do you mean "runs pretty good at highway speed"? Is it running smooth without missing? Is more throtle then necessay required to get it going?
Do what Allen suggests--that'll get you to the basic problem. To me it sounds like plugs and wires--when did you last tune it up. That means change plugs, wires, rotor and cap?

Greenday · Oct 26, 2011

idle air control or throttle position sensor!

Stephen Newell · Oct 26, 2011

I have a 93 Chev van that was doing that. I started searching for a fuel or emission control system problem. I ended up spending five to six hundred dollars replacing parts one at a time to find out it was the ignition control module.

Anonymous-0 · Oct 26, 2011

Follow the KISS principle. Run a good compression test first. Make sure the engine is sound. Second use a good scan tool. Many conditions will not set a check engine light. Data stream can be very helpful. I have plenty of people who come in to my shop for diagnostics and then do the repairs them selves. You may want to invest in an hour of diagnostic time. That said, all of the suggestions are real possibilities given your description of the problem.

McRay · Oct 26, 2011

try replacing rear plugs - at low speed it could be the transmission torque converter shutter with bad plugs and wires.

Mike in Mn. · Oct 26, 2011

Sounds like the EGR valve to me, unhook it and see if that helps, sometimes the seat erodes and even unhooked doesen't make a difference . Cut a piece of tin and slip it under and seal the passage off.

okierob · Oct 26, 2011

Ok, i unhooked the EGR and pluged the line, it ran a lot better. It seemed to need a little extra throttle out on the road with it unhooked. I had'nt drove this truck for many yrs. It has been sitting at my Dads.

This truck has been sitting for years. It had developed this problem prior to being parked.

I did change 2 plug wires thanks to mice. I have a new set of plugs, yet to be installed.

I assume the EGR was opening to soon, or weak spring,bad diaphram,etc. I'll get a new one ordered.

This is not a have to get it done as soon as possible project. I'll work on it as i can.

Hopefully the new Valve and plugs will get it running smooth.

Thanks for the suggestions, I'll keep the updates coming.

Errin OH · Oct 26, 2011

I have to agree with Allan, you really need to start at square one and trouble shoot the issue.

But here is another one I have found along the way.

Old truck that had several hunderd thousand miles. Check engine on permanently. Truck would not idle or if it did was rough. Touch the pedal and it would die unless you got on it pretty hard. Made for backing up to a trailer pretty tough.

Long story short, one of the injectors had a bad o-ring. Tail pipe was full of black soot. If you watched the mist from the injector while running you could see steady drops of gas.

Rough idle was running to rich. Crack the throttle plate and you flooded it out. Step on it and open it enough it would get enough air to catch up and stay running (usally tires start spinning).

The first fella replaced $500 worth of parts before giving up and selling to my buddy for said $500. My buddy was determined to do the same $500 bucks worth of parts, but I stopped him at $100 when he called and asked how hard was it to replace the computer.

bdpayne · Oct 26, 2011

ok due to the fact it has set for a while running at idle look in the throttle bores check for excessive fuel if so could be inj o-rings or the fuel preasure regulator. kit for the regulator is cheep and could cause the problem as it did on mine once.

Brad

banjo · Oct 26, 2011

After bypassing the Egr, Changing the plugs, it idles,takes the throttle, and runs smooth down the road.

okierob · Oct 26, 2011

Allen, it never did set the check engine light. I dont know if the bulb is bad or not.

Like i posted up top. After bypassing the EGR, changin the plugs, it runs pretty darn good. Thermosatat is sticking even after changing. Once it warms up and opens the first time it appears to work normally.

This is a work in progress, this truck needs some going over. But it was bought new by my grandpa and has been in the family the whole time.

It has been parked sine 2007. I just brought it home and started to see what all it needs to get it back on the road.

Allan in NE · Oct 26, 2011

Rob,

Just turn the key to the run position. That light should light (upper right corner of the cluster) and then go out when the engine starts.

If it doesn't, the bulb is toast and you've just simply GOT to have that light. Thru it, you can see the codes and it will tell you whenever there is something wrong. Further, it will tell you when the computer is in "limp" mode.......just throwing fuel at the engine to keep it running.

Sounds like you're gettin' 'er handled,

Allan

Janicholson · Oct 26, 2011

The last one I fixed with the throttle reaction you describe had a bad throttle position sensor. It would run, but off idle it was bad as can be to get it to get to speed (then it was better, but nor as it was originally. Jim

Bob · Oct 27, 2011

SOMETIMES, "fixes" can be SIMPLE.

You had the CLASSIC sumptoms of an Chevy 5.7 EGR problem and others tried to make it a more complicated deal!

1988 Chevy trouble

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