'88 Sierra 2500 sometimes dies at low speed.. help? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Rick Johnson · 04-27-2001, 07:39 PM

I'm new to this board, so please bear with me. Often, when I apply the accelerator and let up, the engine acts like it's going to die. And sometimes it does. However, if I touch the accelerator a bit before it has a chance to die, then the engine will speed up and run normally... I just tap it a bit. I've changed plugs, but that doesn't seem to help. Is this a vacuum problem? Anyone else have this problem? Thanks. Rick

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Rick and Kate Johnson
Burns, Oregon
'88 GMC 2500

Z16 · 05-04-2001, 10:33 AM

Could be any number of sensors, but a guess would be the throttle position sensor (TPS). Best thing to do on a computer truck is to have a mechanic download trouble codes. He may need to drive the truck while the scan tool is hooked up to recreate the problem. You can find the trouble codes in a shop manual ( not sure if GM manuals, but Chiltons and Hanes) and can test with just a test light.

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71 Sierra
98 Sierra

Rick Johnson · 05-04-2001, 10:57 AM

Thanks, Z16. I'll check out the TPS. I sprayed down the throttle body well with carburetor cleaner, and that helped a bit, but not entirely. Haven't checked, yet, to see if this truck has an O2 sensor, but if it does, I'll probably check that, too. Is there some way I can get the engine code readout, myself, without having to take it to a mechanic? We live 30 miles out in the country, and I prefer to do things, myself, if at all possible. Thanks again for your help. This board has a nice group of people. kind regards, Rick

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Rick and Kate Johnson
Burns, Oregon
'88 GMC 2500

Buffalobob · 05-04-2001, 04:25 PM

Howdy Rick

Shucks or most auto stores carry them code readers. I think they're about 20 or maybe 30 bucks. They come with instruction manual and work for many different gm vehicles. the manual has the diagnostic codes and their meanings for the different vehicles. Theres a socket under the dash on driver side that it plugs into. Get one, it's easy to use, and use it just once and it paid for itself many times over!!

Chevyman69 · 05-05-2001, 06:36 PM

The easiest way to read codes is to look under the dash and find the 12 pin computer connector. The two terminals on the upper row of terminals on the right side is the ground and diagnostic terminal. Just take a wire and join the two together and turn the key on. The service engine soon light will flash in code, beggining with code 12 flashed 3 times then any trouble codes present and then endiong with code 12 flashed 3 times.

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69 CST, 402 steel crank, heavy rods polished ported heads 2.19/1.88 should be 450+ 700R4 373 Posi buckets/console air/tilt/tach 4wheel discs
Daily Driver: 92 Chev 4x4 350 Accel filter/cap/rotor/coil Edelbrock intake and headers true duals Helix TBI spacer stock 700R4 for now!

c_lorencz · 05-05-2001, 07:09 PM

Or you could spend 5 grand on a snap-on OBD scanner

Seriously listen to chevyman69 he knows his computers

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'84 Sierra: '78 chev SB 400:
Steel crank,Drop forged rods, and pistons,
Crane .477/.481 hyd roller cam
Manley 1.50/1.94 valves
Edelbrock Pro Ram 2 blower intake
underneath dual Holley 390 cfm carbs,
Stock 350 turbo tranny
Daily driver: 94 Pontiac trans sport minivan

Rick Johnson · 05-11-2001, 11:58 AM

Hello again. I followed advice on checking trouble codes by connecting diagnostic and ground pins, then turning the ignition key on (thanks, Chevyman69).

Thought it would be best to see what codes are stored before launching into any fix.

Only code 12 showed up. Did it twice.

There are several TPS and other sensor (like o2) faults that should store trouble codes. So, if these components are faulty why aren't there any codes stored? (FYI, I did run the engine and drive the rig to recreate the problem right before checking, and I didn't disconnect the battery, which would have erased the trouble codes according to the Haynes manual.)

Could it be a timing problem? The troubleshooting section in the front of my Haynes manual seems to point to that...

I'll check the TPS, as Z16 suggested (thanks). I can check to make sure the TPS is fastened and tightened correctly, but how do I check to see if it's working ok? (Aside from replacing it with a new part... the ole "switch-'em-out-one-at-a-time" approach...)? Maybe just connecting and disconnecting it with the engine running to see if there's any difference? Would that be an acceptable approach? Or would that damage the computer? Feedback appreciated here...

Also, how can I test the o2 sensor to see if it's faulty (again without buying a new one)?

If it isn't the timing, and it isn't the TPS or the o2 sensor, what else should I check?

Could it be some EGR problem as was suggest to DennyB for the problem with rough and fast idling?

Thanks for your insights... I really appreciate the help and wisdom on this board.

Kindly, Rick

------------------

Rick and Kate Johnson
Burns, Oregon
'88 GMC 2500

04-27-2001, 07:39 PM	#1
Rick Johnson Registered User Join Date: Apr 2001 Location: Burns, Oregon, USA Posts: 3	'88 Sierra 2500 sometimes dies at low speed.. help? I'm new to this board, so please bear with me. Often, when I apply the accelerator and let up, the engine acts like it's going to die. And sometimes it does. However, if I touch the accelerator a bit before it has a chance to die, then the engine will speed up and run normally... I just tap it a bit. I've changed plugs, but that doesn't seem to help. Is this a vacuum problem? Anyone else have this problem? Thanks. Rick ------------------ Rick and Kate Johnson Burns, Oregon '88 GMC 2500 __________________ Rick and Kate Johnson Burns, Oregon '88 GMC 2500

05-04-2001, 10:33 AM	#2
Z16 Registered User Join Date: Mar 2001 Location: Medicine Hat, Alberta, Canada Posts: 1,508	Could be any number of sensors, but a guess would be the throttle position sensor (TPS). Best thing to do on a computer truck is to have a mechanic download trouble codes. He may need to drive the truck while the scan tool is hooked up to recreate the problem. You can find the trouble codes in a shop manual ( not sure if GM manuals, but Chiltons and Hanes) and can test with just a test light. ------------------ 71 Sierra 98 Sierra __________________ 98 GMC Sierra Ex Cab, cowl hood, Euro LED lights, 30 bar billet, Whipple Supercharged 350 Vortec: Forged flattops, E-Tec aluminum heads, Comp Cam, Scat crank and rods, Granatelli Mass air flow, Headers, Flowmaster exhaust , Complete MSD Ignition, Custom Tuning, intake spacer , ported throttle body, AC Delco port injection upgrade, Roller Rockers, Power Pulleys. Gear Vendors Overdrive. Soon to hit a dyno. 2/4 drop(for now). 95 Chevy S-10 Ex Cab 4.3 5 Speed 2/3 drop, Euro lights, billet grill, More to come. The Daily Driver

05-04-2001, 10:57 AM	#3
Rick Johnson Registered User Join Date: Apr 2001 Location: Burns, Oregon, USA Posts: 3	Thanks, Z16. I'll check out the TPS. I sprayed down the throttle body well with carburetor cleaner, and that helped a bit, but not entirely. Haven't checked, yet, to see if this truck has an O2 sensor, but if it does, I'll probably check that, too. Is there some way I can get the engine code readout, myself, without having to take it to a mechanic? We live 30 miles out in the country, and I prefer to do things, myself, if at all possible. Thanks again for your help. This board has a nice group of people. kind regards, Rick ------------------ Rick and Kate Johnson Burns, Oregon '88 GMC 2500 __________________ Rick and Kate Johnson Burns, Oregon '88 GMC 2500

05-04-2001, 04:25 PM	#4
Buffalobob Registered User Join Date: Jul 2000 Location: Jefferson City, Montana Posts: 32	Howdy Rick Shucks or most auto stores carry them code readers. I think they're about 20 or maybe 30 bucks. They come with instruction manual and work for many different gm vehicles. the manual has the diagnostic codes and their meanings for the different vehicles. Theres a socket under the dash on driver side that it plugs into. Get one, it's easy to use, and use it just once and it paid for itself many times over!! __________________ 72 C20 Camper Special all original sweet truck 71 C20 slightly built 350 68 K10 (terrible mods needs restore) 68 K10 (less engine) 67 C10 on 78 K10 frame 68 K20 frame/chasis

05-05-2001, 06:36 PM	#5
Chevyman69 Vortec 350's Suck Join Date: Nov 2000 Location: Pickardville Alberta Canada Posts: 544	The easiest way to read codes is to look under the dash and find the 12 pin computer connector. The two terminals on the upper row of terminals on the right side is the ground and diagnostic terminal. Just take a wire and join the two together and turn the key on. The service engine soon light will flash in code, beggining with code 12 flashed 3 times then any trouble codes present and then endiong with code 12 flashed 3 times. ------------------ 69 CST, 402 steel crank, heavy rods polished ported heads 2.19/1.88 should be 450+ 700R4 373 Posi buckets/console air/tilt/tach 4wheel discs Daily Driver: 92 Chev 4x4 350 Accel filter/cap/rotor/coil Edelbrock intake and headers true duals Helix TBI spacer stock 700R4 for now! __________________ 69 Chev CST 10 reg cab lwb Daily Driver: 92 Chev Reg Cab LWB Silverado 4x4, K.I.A 7:51 AM 04/22/03 Will be resurrected

05-05-2001, 07:09 PM	#6
c_lorencz Registered User Join Date: Dec 2000 Location: Alexander,Manitoba,Canada (and no i'm not slow) Posts: 65	Or you could spend 5 grand on a snap-on OBD scanner Seriously listen to chevyman69 he knows his computers ------------------ '84 Sierra: '78 chev SB 400: Steel crank,Drop forged rods, and pistons, Crane .477/.481 hyd roller cam Manley 1.50/1.94 valves Edelbrock Pro Ram 2 blower intake underneath dual Holley 390 cfm carbs, Stock 350 turbo tranny Daily driver: 94 Pontiac trans sport minivan __________________ '84 Sierra: '78 chev SB 400: Steel crank,Drop forged rods, and pistons, Crane .477/.481 hyd roller cam Manley 1.50/1.94 valves Edelbrock performer intake underneath a 600 Holley DP Stock 350 turbo tranny Daily driver:94 Pontiac Firefly

05-11-2001, 11:58 AM	#7
Rick Johnson Registered User Join Date: Apr 2001 Location: Burns, Oregon, USA Posts: 3	Hello again. I followed advice on checking trouble codes by connecting diagnostic and ground pins, then turning the ignition key on (thanks, Chevyman69). Thought it would be best to see what codes are stored before launching into any fix. Only code 12 showed up. Did it twice. There are several TPS and other sensor (like o2) faults that should store trouble codes. So, if these components are faulty why aren't there any codes stored? (FYI, I did run the engine and drive the rig to recreate the problem right before checking, and I didn't disconnect the battery, which would have erased the trouble codes according to the Haynes manual.) Could it be a timing problem? The troubleshooting section in the front of my Haynes manual seems to point to that... I'll check the TPS, as Z16 suggested (thanks). I can check to make sure the TPS is fastened and tightened correctly, but how do I check to see if it's working ok? (Aside from replacing it with a new part... the ole "switch-'em-out-one-at-a-time" approach...)? Maybe just connecting and disconnecting it with the engine running to see if there's any difference? Would that be an acceptable approach? Or would that damage the computer? Feedback appreciated here... Also, how can I test the o2 sensor to see if it's faulty (again without buying a new one)? If it isn't the timing, and it isn't the TPS or the o2 sensor, what else should I check? Could it be some EGR problem as was suggest to DennyB for the problem with rough and fast idling? Thanks for your insights... I really appreciate the help and wisdom on this board. Kindly, Rick ------------------ Rick and Kate Johnson Burns, Oregon '88 GMC 2500 __________________ Rick and Kate Johnson Burns, Oregon '88 GMC 2500



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