1995 Sub 2500 no low idle or trans shift

3144 Views 7 Replies 3 Participants Last post by ChevyFan, Jul 4, 2014

jlee804

Discussion Starter · Apr 24, 2006

Hi am new to the Sub Forum. I think these auto forums are great because of the vast knowledge people are willing to share and help other.

I own a 1995 3/4 7.4 Liter Sub. Love the vehicle

and in the 11 years it has not given me any problems -- until now

. I have 70k on the vehicle and yesterday after a Sunday drive and gas fill up, the motor will not go into a slow idle when the engine is started. The vehicle will not also shift out of 2nd gear. These 2 problems started at the same time. I am thinking it is a vacuum leak, but don't know where to start. I did a quick glance over the motor but did not find any loose hoses. Has anyone ever ran across these problems?

Thanks

Jerry

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ChevyFan

· #2 · Apr 25, 2006

Hey, welcome to the Suburban Club.

Wow, 70K on a 1995? That's pretty low miles. As for your issues, what does the vehicle do? You start it up and it stays on the fast idle? When driving, it goes between 1st and 2nd gear fine but it won't go into 3rd?

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jlee804

Discussion Starter · #3 · Apr 25, 2006

Thanks for the Welcome. Yeah it is pretty low miles. I only use it mainly to out of town trips so most of the miles are freeway. Yes I start it up and it stays at fast idle around 1200-1500 rpm. Usually it drops down to 800-900. As for gears I can't tell if it is 1st or 2nd. I think second cause I can do 35-40mph and the car is tac is around 2200-2500 rpm. Unless 1st gear can give me that range of RPM, but I would think the engine would tac higher with a 4.11 rearend.

Steve said:
Hey, welcome to the Suburban Club.

Wow, 70K on a 1995? That's pretty low miles. As for your issues, what does the vehicle do? You start it up and it stays on the fast idle? When driving, it goes between 1st and 2nd gear fine but it won't go into 3rd?

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· #4 · Apr 25, 2006

You're probably looking at an idle speed sensor that is in the process of failing. The 4L80E trans relies on this sensor to help it guage it's shifts. Sometimes when they start to fail, and your tranny shifts, it feels like someone just gave you a good solid boot in the ass. They will not always trigger a check engine light. Is your engine light currently lit when you drive it?

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jlee804

Discussion Starter · #5 · Apr 26, 2006

TrailLeadr said:
You're probably looking at an idle speed sensor that is in the process of failing. The 4L80E trans relies on this sensor to help it guage it's shifts. Sometimes when they start to fail, and your tranny shifts, it feels like someone just gave you a good solid boot in the ass. They will not always trigger a check engine light. Is your engine light currently lit when you drive it?

Thanks for your reply. Currently there is no check engine light lit when the engine is started. i will have to look up the idle speed sensor. Do you happen to know where it is located? I was also thinkig about buying a reader that you hookup to the car and check for error codes if one is available for a 95 sub.

Jerry

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jlee804

Discussion Starter · #6 · May 25, 2006

1995 Sub 2500 no low idle or tans shift

jlee804 said:
Hi am new to the Sub Forum. I think these auto forums are great because of the vast knowledge people are willing to share and help other.

I own a 1995 3/4 7.4 Liter Sub. Love the vehicle and in the 11 years it has not given me any problems -- until now . I have 70k on the vehicle and yesterday after a Sunday drive and gas fill up, the motor will not go into a slow idle when the engine is started. The vehicle will not also shift out of 2nd gear. These 2 problems started at the same time. I am thinking it is a vacuum leak, but don't know where to start. I did a quick glance over the motor but did not find any loose hoses. Has anyone ever ran across these problems?

Thanks

I took my sub to a shop and the problem ended up being the computer chip was bad. A new chip was installed and programmed to factory and the sub runs perfect! Cost was $250.00, so I was happy about that.

Jerry

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Butters_AF

· #7 · May 29, 2006

Problems with K2500

jlee804, I've also got a K2500 3/4 4X4 that seems to have the same problem. I just wanted to see if I have the exact same problem and if so, what exactly did they replace.
My vehicle, out of seemingly nowhere, started idling @ 1200 - 1500 RPM, also, it wont shift out of 2nd gear while driving anywhere.
If I disconnect the battery for 10 min. to reset the computer it runs fine until what I believe is it's diagnostic period is over, then back to the same old problems.

Please elaborate on you problems and solution, it would be much appreciated.

Thanks,

Butters_AF

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ChevyFan

· #8 · Jul 4, 2014

Someone trying to bring this post back to life?

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