1995 Chevy 305 TBI HELP!  
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1995 Chevy 305 TBI HELP! - 12/24/2007 3:38:26 PM   
Jazzy



Posts: 1097
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline
OK. The basics: 130K+ miles, original O2 sensor, 6-7 year old throtle position sensor.

The problem: During engine warm-up idle is normal. This means that if it is real cold outside (winter) the idle is somewhere around 1K. If it isn't real cold the idle stays around 7.5K. After initial warm-up (engine temp still not enough to pop t-stat) idle drops to normal levels - around 600 rpm. All this is good and dandy until engine is fully warmed up/hot.
After t-stat pops and engine is at normal operating temp the idle jumps up to around 1K. Giving the throttle a good goose will drop it back down to around 600 RPM. However, when a little gas is applied and released the idle jumps back up to 1K! Give it a good goose and it drops back down. A little gas and it jumps back up. It does this even after a fair amount of city or highway travel. Without giving the gas pedal a stomp the idle will not drop back down.

What is causing the throttle to jump back up (or not letting it drop back down)?!
Is there an engine temp sensor that could be going bad?
Could it be as simple as sparkplugs? (They're Bosch platinum with multiple ground electrodes. About 1.5 yrs old.)

Being that the engine is in a 5-speed manual 4X4 pickup this is getting to be a PITA!!

Anyone have any ideas?

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RE: 1995 Chevy 305 TBI HELP! - 12/24/2007 3:43:22 PM   
guver


 

Posts: 8541
Joined: 3/7/2003
From: LaGrange, OH, USA
Status: offline 		It sounds like more of a mechanical problem rather than a control/electrical/computer problem.

One way to tell is to get it acting up and inspect the stop to see if there's clearance in between or simply pull the throttle towards closed position. Sometimes pushing the butterfly shaft sideways will imediately make it drop to the stop or control motor/soleniod.

If it is indeen a mechanical problem then maybe some wd-40, cleaner, spring, cable, pedal , ect will fix it.

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RE: 1995 Chevy 305 TBI HELP! - 12/24/2007 3:58:51 PM   
nicklambert



Posts: 135
Joined: 4/20/2007
From: joilet, IL, USA
Status: offline 		fuel injectors maybe need to be cleaned? throttle getting stuck maybe? ill have to ask a few people here not really sure.

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RE: 1995 Chevy 305 TBI HELP! - 12/24/2007 11:27:58 PM   
Slammed



Posts: 253
Joined: 5/24/2007
From: Vernon, CT, USA
Status: offline 		its the TPS for sure

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RE: 1995 Chevy 305 TBI HELP! - 12/27/2007 10:40:57 PM   
Jazzy



Posts: 1097
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline 		Well guys, my initial thoughts were that it was the TPS. Given the symptoms, I don't think so. If it were the TPS, why does it only do it when it is at normal operating temp? The first time I replaced it it definately did not care what temp the engine was.

Everything was sprayed with WD and CorrosionX. The linkage moves quite freely and smooothly.

After speaking with a buddy, the idea of a vacuum leak of some kind came to mind. Then I remembered that while replacing the throttle body-intake manifold gasket last year (now THAT was a huge vacuum leak!!), the EGR valve was thought to be an issue. I think it may be sticking now. Since I have a new gasket it may be time to replace or free it up.


Thanks for the ideas so far!
Hope everyone had a good & safe Christmas! :-)

Any more ideas before I climb into the engine compartment?

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RE: 1995 Chevy 305 TBI HELP! - 12/29/2007 10:25:43 AM   
rideicon



Posts: 287
Joined: 2/16/2007
From: anderson, CA, USA
Status: offline 		Im not sure the EGR would cause that, but it would be a good idea to buy some vacuum line and re-do all the lines, any hair crack can cause the engine to run funny and its usually easier to replace EVERY LINE than it is to replace the bad looking ones and try to figure out if some are okay or not cuz sometimes heat can cause the hairline crack to open, and even if its got it you may not see it..
I'm going to guess vacuum or something with the cooling system, man i haven't touched a tbi small bock in years... its always a good idea to clean the throttle body really well, make sure the egr is connected sealed on the intake side of the filter so it actually got some vacuum on it, should be a good start

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RE: 1995 Chevy 305 TBI HELP! - 12/29/2007 2:08:40 PM   
bigcam


 

Posts: 66
Joined: 11/13/2004
From: York, PA, USA
Status: offline 		I'm not familiar with GM engine controls but no one has mentioned anything about idle air control. IF GM uses a device to change the amount of air going into the engine at idle speed (not throttle plates) and this is controlled by the processor, I would check, clean this device and make sure is is working to spec. Just a thought from a FORD guy.

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RE: 1995 Chevy 305 TBI HELP! - 12/31/2007 8:15:10 AM   
timmy45140



Posts: 135
Joined: 2/18/2005
From: Hamilton, OH, USA
Status: offline 		At the rear of your TB there is a vacuum line that goes to the MAP sensor. On a visual inspection it may appear to be ok, but is more than likely dry rotted. The idle air control is another point to check on, like bigcam said. It's located on the passenger side of the TB. It's a cylindrical tube looking part with a plug with 3 wires. Your EGR valve is controlled by the ECM via a solenoid in between the TB and EGR valve. Hook up a vacuum tester and pull a vacuum on the egr. If it doesn't hold a vacuum it's bad. Another possibility is carbon buildup in the EGR itself and a piece of carbon buildup has lodged itself in the EGR itself and is preventing it from fully closing. A quick fix for this is to remove the EGR and clean it with carb cleaner and a wire brush. Don't forget to clean the EGR port on the engine the same way. Hold off putting the EGR back on and attempt to start the engine to blow out all the excess carbon deposits. This should give you a head start. I've listed potential problems in order from most common to least for the problem you stated. If you have anymore questions feel free to PM me.

Tim

< Message edited by timmy45140 -- 12/31/2007 8:17:22 AM >


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RE: 1995 Chevy 305 TBI HELP! - 1/1/2008 9:10:32 PM   
Jazzy



Posts: 1097
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline 		Thanks for the tips guys! When I get some time and feel like braving the weather I look over everything.

Thanks again and Happy New Year!

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