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weird rpm issue..

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Posted by: devilchild

i was driving the other day in my 96lsc and noticed that the rpm's got "stuck" at about 1500... i could rev higher.. but they would not drop lower.... so i just coasted to the next stop light and had to hold the brakes harder as the rpms were still at 1500 and i could feel the car pulling a little... so i punched it on green for a few secs. and it stopped..??(dropped to the normal under 1000 at idle)

it was really cold out and i didnt let the car warm up for the usual 10 mins..

happened again ... again didnt let the car warm up for more than 5 mins.. and again took me revving the engine once or twice to get it to stop.

throttle position sensor??.. some sort of idle sensor??.. cold weather??

car is chipped .. and i chipped it pretty much soon as i got it ..so i did not notice if it did this before..

just seeing if anyone else had this happen..

Posted by: unity

Weird, this exact same thing happened to me just a few days ago. Thought the throttle cable got stuck. But after pulling into my work lot, I killed the engine and started it up and it was fine.

Posted by: 93zzzt

i havent had this happen in my mark yet, but i've noticed a lot of weird

in my lightning that starts when the gas stations start with the winter blend fuel.

could be that.

Posted by: unity

Oh, and I have a chip also....

Posted by: mespock

I think Ray has a solution for the stuck tac...

Posted by: unity

But I dont think its a stuck tac, the car is holding RPM. I could not even lock my brakes!

Posted by: mmtphoto

I vote IAC-do the seafoam thing, and after that, disconnect the battery pos and neg cables and clamp them together for 15 minutes-it has happened a few times to me, twice on my 93 and once on my 96. good luck, pray you don't have to replace it.

Posted by: Dawkins

+2 Seafoam

Posted by: unity

Clamp the pos and neg together? You do realize some systems remain active for a while after the battery is disconnected, such as crash bags. I really would not recommend that.

As for Seafoam, it wont even get to the IAC unless you put it into the intake tube which can be VERY hazardous to the MAF sensor. Remember the IAC is on the throttle body. Typically one "injects" Seafoam after the TB directly into the intake manifold.

Posted by: mmtphoto

Quote:

Originally Posted by unity

Clamp the pos and neg together? You do realize some systems remain active for a while after the battery is disconnected, such as crash bags. I really would not recommend that.

As for Seafoam, it wont even get to the IAC unless you put it into the intake tube which can be VERY hazardous to the MAF sensor. Remember the IAC is on the throttle body. Typically one "injects" Seafoam after the TB directly into the intake manifold.

I've done the battery thing a few times, it does reset the sensors/ECM so that the systems have new baselines (relearn process). Nothing blew up...
As for the seafoam, I remove a vacuum line on the intake and inserted it into the bottle-don't see how exactly that might affect the MAF sensor (nowhere near it) and since this intake location is relativly close to the IAC, I'd bet it has some positive cleaning effect on it-seemed to work for me. There are instructions on the can to do this, and you can rent out your Mark as a skywriter when you restart it

. Worked for me (three times in five years of Mark ownership, two different models), and mine idles great.

Hope yours will soon too, whatever your problem is..

Posted by: unity

If you read my post, you would see that I said IN ORDER to clean the IAC with Seafoam you would have to use the intake method, which could mess up the MAF via leak down. This is not the preferred method, but there is not other way Seafoam would get through the IAC.

And going in via intake will not get anywhere near the IAC, period. Believe me, I very much know Mark VIIIs and how the intake system works.

I still would not recommend connecting the two terminals. First, just disconnecting the battery for even a minute will clear codes. I've done this in order to do so. Second the crash bags still hold a charge, even without the battery. Connecting the two terminals could damage the capacitive system.

Posted by: mmtphoto

lucky for me, I did not have that problem again on my 96, I guess I was just fortunate that I didn't cause other problems

. Maybe the IAC was not the problem on mine. but that's exactly like what was happening to mine-high idle all of a sudden, so much I had to stand on it at stops. I remember when it happened on my 93, stopping in a parking lot and looking to see if the throttle cable was hung up. I was later convinced that it was the IAC after going on this and other forums, and those fixes were found either here or some other forum, I'm just glad it worked. I occasionally still put a can of seafoam in the tank, and once or twice a year I will induce a half a can or more into the intake. If I have doubts, I'll do the battery cable thing, and have never experienced a problem. Because of where the throttle body is, I have no interest in pouring anything down there, I have only sprayed TB cleaner there, and that is only when I'm motivated enough to do so. I do not want to have to remove and replace the IAC, so I'm ahead so far (going on 6 years/about 70,000 miles total).

Posted by: mikemark8

[quote=unity;343228]Clamp the pos and neg together? You do realize some systems remain active for a while after the battery is disconnected, such as crash bags. I really would not recommend that.

Jim Grant's Tech Tips (Alldata subscription service)

Computer Dumping
Q: I would like to know if you have any opinions on dumping the computer by taking the negative terminal off and touching it to the positive for 20 seconds to clear the computer of any stored codes. If so, will a vehicle that’s equipped with air bags, possibly deploy the air bag?

A: Actually it’s a common practice to disconnect both battery terminals and not only hold them together but to connect them for the duration of the service being performed. For example when servicing the air bags some vehicles require the battery cables being joined for 15 minutes to a half hour before performing service or repairs that involve the air bag system. It is not uncommon for today’s vehicles to have several computers on-board. Inside the computers there are capacitors that will hold/store electrical energy. Connecting the battery cables provides a means of dissipating this stored energy without causing any harm. In most cases (not all vehicles) the software to operate the systems is not volatile and will be safely retained in the computer/s. If you have an anti-theft radio be sure you have the radio code so it can be reactivated.

Posted by: unity

[quote=mikemark8;347396]
Quote:

Originally Posted by unity

Clamp the pos and neg together? You do realize some systems remain active for a while after the battery is disconnected, such as crash bags. I really would not recommend that.

Quote:

Originally Posted by unity

Jim Grant's Tech Tips (Alldata subscription service)

Computer Dumping
Q: I would like to know if you have any opinions on dumping the computer by taking the negative terminal off and touching it to the positive for 20 seconds to clear the computer of any stored codes. If so, will a vehicle that’s equipped with air bags, possibly deploy the air bag?

A: Actually it’s a common practice to disconnect both battery terminals and not only hold them together but to connect them for the duration of the service being performed. For example when servicing the air bags some vehicles require the battery cables being joined for 15 minutes to a half hour before performing service or repairs that involve the air bag system. It is not uncommon for today’s vehicles to have several computers on-board. Inside the computers there are capacitors that will hold/store electrical energy. Connecting the battery cables provides a means of dissipating this stored energy without causing any harm. In most cases (not all vehicles) the software to operate the systems is not volatile and will be safely retained in the computer/s. If you have an anti-theft radio be sure you have the radio code so it can be reactivated.

Quote fro Ford Techs Online:

"I have been told of this 'touching' story many times. It is an Urban Legend and is not true.

For three years back in 1989-1992, one automaker had one model in their line where this technique worked. Since then, vehicles have diodes installed in their electrical systems and the whole idea in now bogus."

Posted by: NateRW21

removing the negative terminal is all that is required. Current flows from negative to positive, removing the positive alone and allowing it to sit will pull the power from the capacitors in the system.

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