Rpm Raises Between Shifts
 

:confused: Alright just bought my first stang and seems to have a minor problem, maybe a vacume leak but can't find anything? While shifting gears when you depress the clutch the RPM's raise by about 500 RPM's in between gears until the clutch is re-engaged (will drop eventually but takes at least 5 sec if you keep the clutch depressed). Also RPM's take awhile to drop to idle when clutch is pushed in rolling to a stop, for about 5 seconds tach will sit at 1500 RPM then finally drop to idle speed or just reving the motor in nuetral gives the same results? This seems to be a intermitant problem but happens more times than not with no particular pattern? Any suggestions on what to check? I have always done most of my engine work myself but dealing with imports (please no remiders of how stupid that was/is), finally realized where real power is made:D

• 95 Mustang Boss
• stock motor with cold air intake
• 3.73's in rear
• off road H pipe - no cats

I would first check your IAC located on your throttle body. Unplug it and see if the problem changes. Either way, I would remove it and clean it with carb cleaner.
Then when you are done, go through the idle reset process as described here: http://www.corral.net/tech/maintenance/idlereset.html

hope this helps

I had a similar problem with my 95 stang. My RPM's would raise as much as 1500 rev's, almost like there was a midget in the eng bay pulling the throttle cable. I also got a check eng light simultaneosly(spelling?) What I had was a dirty throttle position sensor/butterfly valve. If you remove the air intake tubing at the throttle body you will be able to access the inside of the T/B. I sprayed some carb cleaner on the butterfly valve, then moved the valve around to ensure free movement. Worked for me- Oh, one more thing - My car had a sticker on the T/B that said not to spray cleaner into the T/B. Warning you of a protective coating inside the T/B. I never had a prob though. Just some input. Worked for me.

Good luck

Thanks for the advice, will give it a try and see if that clear up the RPM issue. Also just as a heads up I think the warning on the throttle body is because of a teflon coating that is in there to help prevent the butterfly from "sticking". Read a previous post trying to find info on my problem and they suggested cleaning the throttle body with dish detergent and water on a tooth brush to help save the coating - but eiterway don't think it a great difference!

fiveohpatrol - tried that link you provided and it didn't work. Went to corral.net web site to find it but appears they are having a problem with there web page at the moment. Anyway you could give me a quick run down on the idle reset process after I clean the IAC - also what does that stand for?:confused: You'll have to excuse me as I am new to the game! Thanks!

it worked for me, but heres the text from it anyway...

"It seems that many people have trouble with the way their 5.0 Mustang idles. Symptoms are usually a stumbling or rough idle which may be the result of modifications, or any number of other factors that may contribute to the problem. Clogged Emissions Gas Recirculation (EGR) Valves or Idle Air Bypass (IAB) solenoids are often to blame. A bad Throttle Position Sensor (TPS) will cause the engine to "hunt" for a proper idle setting.

If you are experiencing idle problems first check the IAB. If it has large amounts of carbon deposits in it you may need to clean it using regular carburetor cleaner. You will have to remove it to do this, DO NOT clean it while it is on the car! If you have checked to make sure that your EGR, IAB, and TPS are clean and properly set and you are still experiencing problems try the following:

1.Clear the EEC-IV's idle memory by disconnecting the battery for 20+ minutes.
2.Disconnect the Idle air bypass solonoid
3.Reconnect battery
4. Start engine and set idle speed to desired RPM with stop screw on throttle body (900 rpm works great with E303 or larger cam)
5. Turn off engine and reconnect the air bypass solenoid
* set TPS to 0.90 - 0.95 volts (Do not exceed 1.0 volts MAKE SURE!) Use a digital volt meter!
6.Start engine and let it idle for 2 minutes with no accessories on.
7. Turn off engine for two minutes
8. Start engine again and run for 2 minutes with every accessory turned on.
9. Turn engine off again.

Your computer should have now re-learned the new idle settings. This procedure assumes that you have a clean IAB valve. If it is carboned up then you may need to remove it and clean it with carburetor cleaner. "

This process always works for me.

btw, some call it the IAB, some call it the IAC, (idle air control/bypass) It is a computer controlled "valve" that allows air to enter the engine pass the throttle body depending on different conditions. If it is stuck open, and needing cleaned, it will cause a high idle.

Good deal - prob wouldn't be too bad of a idea to check, clean, or replace those items anyway since I don't know what the guy did before me in the way of mods and maintenance - do know a different intake (Cobra) and b303 cam were in that car at one time before I bought it - now has been returned to stock intake/cam, not sure why they went back to stock? Thanks again!

make sure the clutch cable is adjusted right, especially if it has an aftermarket firewall adjuster and/or cable and quadrant.

My car does it too, to an extent. It does it in cold weather (below 40 - Florida). It will blip up about 500 RPM's between shifts. In any weather though, my RPMS won't drop below 1150 while coasting to a stop with the car out of gear. About a second after I stop completely, It drops back down to normal. Is this normal, or just another form of the same symptom? I clean my MAF, TB, and IAC regularly, but have never cleaned the EGR. Engine is stock.

In a nutshell that is the same exact thing my car is doing - not a big deal but gets annoying. Seems to happen after the car has warmed up, paid closer attention to it last night coming back from work. I plan on going through everything Friday afternoon - will let you know what I find!

huh?
 

Ummm...what does the clutch have to do with a surging idle??

READ THE TITLE! SIMI! "between shifts", NOT "surging idle" anytime shifting is involved....???

my pedal was out of adjustment at the firewall adjuster, and engaged the clutch bye just barely touching the pedal, therefore throttle wasnt shut all the way when i depressed the clutch, making it rev....just a thought, wont hurt to consider it mr simi sir...:rolleyes: :rolleyes:

OK
 

I READ THE TITLE Coupe50h! Thanks buddy. I would hope someone would know if there clutch was out of adjustment and the cause for raise in RPMs in between shifting was their frickin foot on the gas pedal!! :rolleyes: :D That's something that anyone that knows their car should feel man...if the clutch was engaging at the wrong place...to soon or too late. Sounds like a dirty EGR, or IAC...TPS out of adjustment...or a sensor sending a signal to the ECU to raise the RPMS for some reason. Take it easy there Hoss. :rolleyes: ;)

Look Simi, he was just suggesting something to look at. We're all here to help eachother out. Alot of the time, someone's past experiences can really help out someone thats having a similar problem.
Sometimes you just have to state the obvious just to make sure.

we're here to help, not make people feel stupid

sorry
 

Yeah, it was just the way Coupe50h came across in his post I guess that sent me on a bad one. Then again, I got a little sarcastice myself. :p Sorry folks. I guess Coupe's suggestion was just a little too obvious IMO...and a could be misleading to some. Many times, on a few mess. boarrds I'm on...I've seen people give wrong advice, which can send someone off on a wild goose chace checking something else that really isn't the problem. And if the person seeking the help is fairly inexperienced...that can confuse things. Some people could & have...taken their cars to mechanics and get bent over to have them check things out, etc. Regards to all... ;) :)

No problem hoSS:cool:
This can still be related all together, a bad signal causing the ecu not reading that the blade is closed between a shift, the clutch can be pressed in too fast, before the ecu realizes the blade is shut, the clutch goes in......ok forget it lol

I think i would know if my foot was still on the throttle while shifting 'hoss'.....i must be doing some kind of decent driving to be clicking off 12's with my combo and gears. thank you;)
carry on..

yep
 

:p I would hope you would know if your foot was still on the throttle when shifting Coupe! That's not what I was saying though...I was referring to SN95BOSS probably knowing if his foot was still on the gas while shifting. I may have misinterpreted your post...but I thought that is what you were basically saying. That maybe he might not know when his clutch is engaging and that his foot is somehow still on the gas. I would think that would be obvious for any of us that know even a little bit about our stangs and know how to drive.
That's a pretty good trap speed for your combo Coupe, considering your gearing. I too can click off 12s...and...11s...:o But I didn't think we were talking about how fast our cars are?? This is turning into a pissing match. I'm done. Sorry if I came off harsh Coupe50h. ;)

Lol, yea i didnt mean to turn it into a piss match, i misunderstood you i guess about the foot on gas thing.....no not harsh, i can handle it:) thanx for the props, my trap is not bad for the gearing and shorty header, and iron heads, but the car is still light at 3100 lbs...i assume you have a gt? that trap speed of yours sounds about right for your combo(those are the heads i wanted:() but im stuck with a budget built high miler:rolleyes: take it easy....

race times
 

Right on...I hear ya. That's some good trap speed for a high mileage engine. Yes, mine is a '90GT. I've got it down to around 3,000 pounds...maybe a little lighter. The scale at the local track seems to be off some lately. I rebuilt my motor about 4 years ago...but it only has around 20K on it now. I drove it on a daily basis only for the first 6 months. Now it's just on the weekends. If I could do it all over I would go with AFR heads and get the intake ported...and a better cam. I know there is better technology out there now than the alphabet cams...but my combo still does pretty good for what it is. I wished I wouldn't have skimped out and went ahead and got things ported during the rebuild...but you know how it goes. I had to draw the line somewhere in the $$$ department. The last couple of times I went to the track though...my trap speed was down 2 or 3mph. I don't know if it was the weather(some wind and humid one of the times), my slicks that are getting old, or my motor somehow getting a tad tired from the nitrous runs. But I've only ran like 3 or 4 bottles through the new motor...and it was built to handle the juice. Who knows. Happy draggin!

Thanks for the info...finally got around to looking into the problem. Ended up being a few things - the IAB (IAC) sensor was carboned up, throttle stop was turned to far in keeping the butterfly open a bit, and the idle needed to be adjust. Also the computer was reset in the process - running perfect now - idle even smoothed out! Thanks again!