5.0_Ceal

Ok!! My 5.0 is giving me trouble and I have NO idea what else to do about it, so ANY ideas are welcome!

It is a 1994 Mustang GT... 5.0 with a manual transmission.

Idle is nice and steady... idles at about 750RPMs or so... but when I give it some gas, as I let go, the RPMs come down slowly but stay at around 1400 for some 2 or 3 seconds, then go back to around 750 or 800 or so... however, let’s say I’m cruising, I put it out of gear and let off the gas pedal... it will stay at around 1400RPMs until it comes to a COMPLETE stop... when it comes to a complete stop, then it’s the same thing, it idles at around 1400 and after 2 or 3 seconds it goes back down...

Next symptom is... when I’m shifting between gears, as I press the clutch pedal, the RPMs go up for a little bit instead of just going down... kinda like if I didn’t take my foot off the gas...

I checked the TPS and the readings were normal I think... with ign on and eng off, I tested at the 3 tps wires, and from one wire I got a constant almost 5V, something like 4.78 or something like that... then from the other wire I got a 1.08 with the throttle closed and it went up to like 4.67 at WOT... engine off. From what I read, that’s supposed to be normal...

The IAC was supposedly replaced by the mechanic with a used but working one... in any case, I took it off to check it and it does look nice and clean...

I also did the idle reset procedure... so the idle is nice and smooth, but the symptoms described above are a real pain and I can’t get rid of them.

HELP OUT PLEASE! I’m about to rip my hair off with this problem lol

mjr46

rip your hair out cause you won't solve the issue, it is the idle dash pot function and is a built in feature with the sn-95's and was done such to lessen clash between gears when shifting hard so as to lessen t-5 warranty claims from hard driving

5.0_Ceal

still, is it supposed to raise the RPMs when I engage the clutch?

mjr46

when you push the clutch in generally it'll raise the rpm's a litttle and hand for a sec or two

5.0_Ceal

but it's not a little... RPMs jump up like 500 RPM or more when I press the clutch pedal... I dunno, seems like an awful lot of wasting gas with the RPMs up all the time...

5.0_Ceal

is this dashpot physical? any chance of it malfunctioning? cause it would seem like it's doing it's job, but VERY slowly... it's job is to bring the RPMs down to idle but smoothly, instead of just dropping them, right? but in this case, it seems like they get stuck and climb down very slowly...

is this dashpot the same as the IAC? or is it some other part or is it something built into the computer?

mjr46

no the dash pot function I believe is a strategy of the ecm, but in any case run a koer test and make sure no IAC codes or anything else exists that'd contribute to the prob

Project 5.GO!

*Disclaimer*
Don't assume I know anything, and I assure you that MJR is much more knowledgeable about this than I am.

Just to throw this out there, I had the same problem with my '89, and replacing the IAC took care of the problem.

When it happened to mine, it was 2 months after I pulled the IAC and cleaned the living crap out of it. After I checked all the other stuff that I was reccommended to check, I wound up buying a new IAC. After I put that in the car, I set the TPS and reset the computer, and it worked like a charm. You mentioned that the mechanic put in a used IAC. Go buy a new one, because they are pretty cheap. Put it in yourself, because it is really simple, and trust me, I know this because -I- can do it! MJR mentioned that there may be something else that is contributing to the computer programming problem, and trust me, a gunked up IAC will really contribute. If that doesn't help, take it off, put it back in the box, and return it! LOL

5.0_Ceal

you can return them for no good reason?? lol I'm thinking about getting a new IAC... the ones for the sn95 aren't that cheap though... about 70dlls at autozone which is the cheapest I found... and I am a student (in Mexico), so 70 dlls is a big deal lol

mjr46

just be careful not to make any evidence of the new one being used so you can return it if it's not gonna solve the issue...=keep the box clean