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Discussion Starter · #1 ·
I have a 91 Silverado K1500 4x4, 5.7L 350, TBI, Auto, 220Kmiles... Its been a great truck, for the most part it runs and drives great! but at low idle or low rpm's it missis,sputters,surges and if im just barely giving it any gas it almost wants to stall out. but it runs great when accelerating or about 60mph and faster almost like nothing is wrong with it. Its had new plugs and wires installed not too long ago, ive changed the fuel filter, took the Idle Air Control sensor out and cleaned it (still might need a new one tho), but ive had people say the throttle body position sensor and also found out maybe the thermostat sensor? This is my first GM but didnt know if anyone had anymore info or could help me out with this a little. Thanks!
 

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Could've had a v8
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Hmm, I'm actually having the same problem although it also will randomly turn on the "service engine soon" light and then do the same thing under acceleration almost like the timing is off. Does yours ever do this? I just turn the truck off and turn it back on and it's okay again. Have you tried replacing the O2 sensor? That's what people keep telling me it is for me but the O2 was replaced a few months back so I don't think that's it. I have also heard that it could be the MAP as well but I'm not sure. I'm not really a guru when it's comes to TBI. I'm used to carbed engines. We might have the same problem so if I figure out what it is for me I might be able to help you out too. Any TBI experts here care to put in their $0.02?
 

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Discussion Starter · #3 ·
my engine light isnt on, those are two other things i have also been told, the MAP sensor and the O2 sensor but havent checked those yet. im going to try and check everything out tomarrow tho but didnt know if i could get anymore ideas or info before then haha. im also getting new exhaust put on the truck soon, its just got the stock single right now but my Y pipe has a bad crack and most of the exhaust is rusted and has fallin off down the road over time so im going with true duals 2 1/4" pipes with offbrand flowmasters but they said that shouldnt change the way the truck runs or mess with the O2s at all with it being on the manifold
 

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I'll Direc your TV
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IAC is bad. Idle Air control valve. Swap that out and that'll solve your problem. It's on the back passangers side of the throttle body
 

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Discussion Starter · #5 ·
yeah, i pulled mine out and sprayed carb. cleaner on it... it was pretty dirty and i got it cleaned up good but the pin inside or valve could possibly be stickin? i might just start buying all new sensors and replace them and hopefully solve the problem?
 

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gun nut
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I had this problem once after reinstalling my distributor i damaged the ignition module this can happen easily the module can over heat causing it to piratically fire. But i also had this problem with my mud truck and it wasn't a oxygen sensor or the ignition module but the vehicle speed sensor if you try to take off fast and it hesitates the ecm (electronic control module) might not know you are moving so its limiting the amount of fuel aloud to the engine causing it to cut out if you are registering speed on the speedometer this isn't the problem.

Do you know how to check you trouble codes??? If not all u need is a paper clip the obd1 port under the dash will have an A and B terminal connect the two with the paper clip and the service engine light will flash once and then two times fast this means 12 so if the light flashes a 42 .... .. the ignition module has a problem.

:confused: shity thing is this could be caused by more than what i have listed
 

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Discussion Starter · #7 ·
yeah, i took it to advance auto and they plugged this thing in (wasnt really a computer because my truck is too old) and the Service Engine light code flashed back everything was good. It runs fine taking off and about 65mph+ it runs great like nothing is wrong, but any speed slower once it gets into Overdrive and the RPM drops it seems to run rough. It also seems to run better when the truck is cold but once it warms up it gets worse. I did find out it was low on coolant and thought maybe the Thermostat Sensor just wasnt reading right but now its full and that didnt do anything. Still tryin to figure it out... too many sensors!
 

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Twin Turbo S-10
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How about the fuel PSI regulator. Spring is known to break on them. take the torq screws out of the top of the TBI and lift up regulator is in the back check spring.
 

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I bet you have a vauccum leak some where. When youre truck is just warming up, its still cold the efi is dumping fuel because its in like "Choke" mode. As it warms up, it leans the fuel air mix out to acomodate warm engine condition driving. So, when its idleing cold its got the fuel to compensate for the extra air leaking in. Also, when you idle the ammount of air and fuel mix is small, less air = less fuel needed for lower engine speed. While your engine is getting more air (vacuum leak) and this little bit of fuel that is being dumped at idle is not enough to creat proper combustion, and could cause your rough running condition. A vacuum leak isnt noticible cruising down the road at 2500 rmp because theres more fuel to compensate. Start looking for cracked hoses or broken plastic couplings in the vac system. Good luck hope this helps.
 

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Discussion Starter · #11 ·
that could be too... its an old truck and some of the hoses look like theyve never been replaced so ill have to check into that. Thanks everyone for the help and advice!
 

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Discussion Starter · #13 ·
my friend that i bought it from, his uncle just did a tune up on it he said but could use a new oil change by now is all. everything else looks good. so far everything looks decent besides some of the hoses which i still havent had time to check for a vac. leak. sucks wakin up early when its dark still and get out and its just getting dark again haha. ill check the cap and rotor tho... never know!
 

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10ptbuck
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Take the egr valve out and see if there is a piece of carbon stuck in it. This would cause a rough idle. Also make sure the gasket is not leaking around the base of the egr valve. These would both cause the symptoms that you are experiencing. Worth checking, just the first thing that came to mind when reading your symptoms.
 

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Cool parts peddler
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Take the egr valve out and see if there is a piece of carbon stuck in it. This would cause a rough idle. Also make sure the gasket is not leaking around the base of the egr valve. These would both cause the symptoms that you are experiencing. Worth checking, just the first thing that came to mind when reading your symptoms.
He is headed you in the correct direction.
Sometimes the EGR valve fails internally and opens to soon.
This can cause the rough run/hesitation you discribe.
Disconnect and plug the vacuum hose to the EGR and test drive the truck a day or so.
If the problem is gone, replace the valve with a DELCO valve. DO NOT use the cheep shit as they can be calibrated wrong an cause more drivability issues.
 

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If the EGR valve is bad you will get code 32. It may not cause the service engine light to come on. My EGR valve is bad and the light doesn't always come. It does cause the problems you are talking about.
 

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Discussion Starter · #19 ·
havent had time to check the EGR yet, work work work... hopefully this Thursday. Wouldnt the code 32 have come up when i took it in and had it checked? Took it to Advance Auto and a guy plugged this thing in and said the code came back clear or that nothin was wrong? or could it just have not read it or picked it up? ill still check into it.. worth a shot!
 
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