anybody else have rpm issue

[sparky]

Just started this recently. When I rev between gears the rpm stays at that rpm, Example, rev to 3500 push in clutch engine stays at 3500, it has alway drop down in rpm. And now when I start engine wheather cold or nomal temp it will rev to 3000 rpm, I have had the truck for 13 years and it has never done this. There is no codes and I have checked TPS, IAC, MAF per my repair manual and all checks good.I don't know what else to do. The truck is 1993 3.0 and 5speed. Other than this the truck runs fine. Any help would be greatful
Thanks Tim

 

[jasonrobo02]

The only way for your engine to maintain a higher speed than idle is for that amount of air to get in. I'd check the throttle cable or the throttle butterfly itself and see if anything is sticking open.

 

[Beef52751]

possibly a vaccuum leak???

 

[sparky]

The only way for your engine to maintain a higher speed than idle is for that amount of air to get in. I'd check the throttle cable or the throttle butterfly itself and see if anything is sticking open.

Ya, I thought of that , I checked it from under the hood and it's not sticking, but I haven't check from driver seat. I'll check that when I get home.
Thanks for the input

 

[NJRanger94]

Its prolly the Iac valve

 

[jasonrobo02]

Its prolly the Iac valve

How can you arrive at that conclusion? He stated that he already performed diagnostic checks on many components including the IAC. Plus, it's my experience that IAC's fail closed, not open which means that your engine stalls or cannot idle when the IAC goes bad.

 

[thegoat4]

I have had the same problem. I noticed that the engine RPM will stay up while I'm rolling but as soon as I come to a full stop it will drop down to idle as it is supposed to. So, it's an electronic problem (bad data to the PCM) rather than anything mechanical. If you have the same behavior, then you can stop looking for mechanical problems.

I haven't had the chance to troubleshoot mine any further than that.

 

[Bob Ayers]

How can you arrive at that conclusion? He stated that he already performed diagnostic checks on many components including the IAC. Plus, it's my experience that IAC's fail closed, not open which means that your engine stalls or cannot idle when the IAC goes bad.

The IAC will not create codes, to see if the IAC is stuck open, unplug the IAC electrical connection, and see what happens to the idle. If the IAC is operating properly, the idle will drop way off when the connector is unplugged.

 

[JP02XLT]

I would also disconnect the throttle cable and make sure its moves free & easy, I had one that started to fray internally & would move free one way & not the other.

JP02XLT

 

[sparky]

Thanks for the replies. The issue has gotton worse, I hate to buy any parts until I know for sure, and when the iac is $64 bucks that hurts. I did unplug the iac when at high idle 3000 rpm and nothin changed, however when the truck came down to normal idle and I unplugged it the rpm dropped but engine did not die. Mechanic friend said iac is bad but I just don't know. Also egr could be bad causing vac leak but I can't find it. Anybody know where it is on 93 3.0? My repair manual shows the 2.3 egr, 4.0 egr but not the 3.0I'm off to search some more.

 

[Froggmann]

If the RPMs didn't drop with the IAC unplugged, then it needs to be replaced or cleaned. It's sticking open.

 

[thegoat4]

Since RPMs didn't drop with the IAC unplugged, you have one of two problems: sticky IAC, or a vacuum leak. Get some B12 and with the engine running spray around major vacuum ports and all of the lines. Unplug the line to the brake booster and plug it up with your finger. If you don't find the culprit then, pop off the IAC and clean it out with the B12. The valve is normally closed and the solenoid has to actively pull it open. During normal driving it actually spends a good amount of time in the open position and if you have gunk in your throttle body, you have the same gunk in the IAC. Be careful about cleaning the throttle body with B12 as it can eat away the epoxy lining if you let it sit in the surfaces for too long. Safer to get some purpose-made TB cleaner.

 

[sparky]

Fixed it. The iac valve sticking open, replaced the iac and it's all back to normal. They proud of the iac tho, I hated to cover it up, after tax $71 bucks. Thanks for all the help.