Go Back   Great Lakes 4x4. The largest offroad forum in the Midwest > 4x4 Talk > Chevy Tech
GL4x4 Live! GL4x4 Casino







Search
Reply
 
Thread Tools
Old August 18th, 2013, 03:48 PM   #1
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
98 gmc

When I start my truck 98 gmc k1500 350 vortec

It revs up to 2000 then goes down to 12-1300 Rpms

But when I'm driveing I can let my foot odd the peddle and it will cruse at 50 because of the rpms staying at 1500.

I'm thinking the tps but I'm not sure and don't want to blindly throw money at it

I need your wisdom people of Great Lakes
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 10:49 AM   #2
Iggy
Senior Member
 
Iggy's Avatar
 
Join Date: 01-02-12
Location: Traverse City, MI
Posts: 109
iTrader: (7)
Check the intake gasket for leaks. I had one that the gasket between the upper and lower plenumn was bad and it did the same thing. The loss of vacuum made the computer think the throttle was open, even though the TPS was fine. It automatically added extra fuel and the rpm's went up. Changed the gasket and the problem was solved.
Iggy is offline   Reply With Quote
Old August 19th, 2013, 03:53 PM   #3
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Like between the plastic part and the intake?
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 06:04 PM   #4
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Well that wasent it so any more ideas?

The tps is only 34$ plus tax but that could be money waisted if its not it
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 06:19 PM   #5
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
Check engine light? You can test a tps with a volt meter. I would guess a vacuum leak. Do the old carb cleaner/starting fluid trick. Spray around the engine with it running and see if the rpm goes up.
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 07:38 PM   #6
Iggy
Senior Member
 
Iggy's Avatar
 
Join Date: 01-02-12
Location: Traverse City, MI
Posts: 109
iTrader: (7)
Like Wheelman said, check the TPS and check other areas for vacuum leaks - that is how I found my plenumn gasket was bad. Like I mentioned earlier, the low vacuum from a leak tricks the computer into thinking the engine needs more fuel.
Iggy is offline   Reply With Quote
Old August 19th, 2013, 08:17 PM   #7
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Quote:
Originally Posted by Wheelman View Post
Check engine light? You can test a tps with a volt meter. I would guess a vacuum leak. Do the old carb cleaner/starting fluid trick. Spray around the engine with it running and see if the rpm goes up.
I did this with no luck. And no check engine light I had it scanned and it said tps
Air idle control valve and one other thing but they can't tell if one thing is causing another thing but I know for sure it's not the air idle control valve
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 08:42 PM   #8
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
Quote:
Originally Posted by muddinman56 View Post
I did this with no luck. And no check engine light I had it scanned and it said tps
Air idle control valve and one other thing but they can't tell if one thing is causing another thing but I know for sure it's not the air idle control valve
Did you test the tps for 5 volts at the harness with the positive probe on the gray wire and the negative on the black. Then back probe the dark blue with the positive probe hook the connector up and turn the key on engine off. Should be 0.6 volts with the throttle closed. Then gradually go up as the throttle opens to 4.5 volts at wide open throttle. If that all test good then the tps should be good.

I am going with vacuum leak or iac motor.
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 08:57 PM   #9
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Iac motor?
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 08:58 PM   #10
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
The Idle air control motor.
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 09:01 PM   #11
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
O haha I thought that to but I checked it and seams to be fine and its 94 bucks lol
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 09:02 PM   #12
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
How did you check it?
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 09:10 PM   #13
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Unplugged it motor revved up.

Unplugged tps nothing happens plus my truck seams to be a little sluggish.
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 09:11 PM   #14
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
Did you test it?
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 09:15 PM   #15
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
No. The only thing I did was pull it off clean it up put it back in.
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 09:17 PM   #16
Wheelman
Extreme Mudder
 
Wheelman's Avatar
 
Join Date: 09-05-08
Location: Pontiac, Michigan
Posts: 271
iTrader: (1)
test it with a volt meter. Super easy to do. No way to really clean it.
Wheelman is offline   Reply With Quote
Old August 19th, 2013, 09:21 PM   #17
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Idk how to set the volt meter to test that or the tps.
muddinman56 is offline   Reply With Quote
Old August 19th, 2013, 09:23 PM   #18
Lousypirate
Bud Light Man of Genius
 
Lousypirate's Avatar
 
Join Date: 02-11-08
Location: Norton Shores 49441
Posts: 8,529
iTrader: (27)
For what it is worth, your vacuum leak could be anywhere.

If that truck has the same vacuum system as all the other vehicles I've owned, you should be able to turn it to defrost after letting it sit all night and hear the vacuum "bleed" off. If it doesn't do that you have a vacuum leak. Not sure where check valves were.

On the old lady's xj, i randomly discovered a vacuum leak on a hard line, so I took some copper tubing and fixed that, added some bling to it too! The hose would have had to have two very drastically different ends, so I took the rubber adapters of the hard line and used copper tubing in it's place. The difference in plugging the hole 1/16" or less in diameter resulted in ~450 rpm difference.

Long story short, don't ever rule out vacuum
__________________
77 Chevy K30 partout thread
94 12v dually partout



Have you given your life up to traction lately?
Lousypirate is offline   Reply With Quote
Old August 19th, 2013, 09:26 PM   #19
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
I sprayed starting fluid everywhere and on every thing with no change
muddinman56 is offline   Reply With Quote
Old August 21st, 2013, 03:07 PM   #20
muddinman56
blood,sweat and beers
 
muddinman56's Avatar
 
Join Date: 10-06-08
Location: armada michigan
Posts: 3,521
iTrader: (18)
Bump
muddinman56 is offline   Reply With Quote
Reply
Great Lakes 4x4. The largest offroad forum in the Midwest > 4x4 Talk > Chevy Tech
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT -5. The time now is 11:55 PM.


Powered by: vBulletin, Copyright 2000 - 2012, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Cracker Enterprises - Powered by Linux
vB Ad Management by =RedTyger=
Page generated in 0.14406 seconds with 50 queries