RPMS dropping fast when I down****

[Paully's5.0]

RPMS dropping fast when I downshift

Hey guys, bought another mustang and have some issues I need help with. After the car is warm, I'll be crusing down the hwy and downshift, my RPMs drop quite a bit. So when I come to a stop, it will sometimes die because the rpms drop so much. I am also have some rough idle issues as well so I am wondering if the two are related.??

Also, the car as a full exahust, and the speedometer cable was changed previously and routed wrong. So there are a lot of sharp bends, plus where the speedo gets near the exhuast, its all melted and I can actually see the cable inside. Hence why my speedo doesn't work. Now I now the VSS may have something to do with my idle and rpm problems, could it be because that cable isn't spinnning that the VSS can't read how fast the car is moving, so it just drops the rpms??

The car has had the emissions equpiment removed, are there any lines, vacuum in particular that need to be closed off or re-routed? I can tell the previous owners had done things to this car half assed so I am wondering if they missed something small like a vacuum line or any nitty gritty stuff.

I dunno, help me out boyz!

 

[Stump1000]

I know on the newer 94up cars, If you unhook the speed sensor when you push the clutch in coming up to a redlight or something the car will stall. If you rev it once right when you push the clutch in it wont die. I dont think the foxes are the same but i could be wrong. I doubt your idle problem has anything to do with the other problem. If you just got the car it would be a good idea to clean the mass air meter. I've seen that fix so many problems, even my own

 

[BlueThunder1988]

Also sounds like the IAC valve may be non-functional... try checking and cleaning it and then adjust the idle.

 

[Rerun]

Also sounds like the IAC valve may be non-functional... try checking and cleaning it and then adjust the idle.

Might even be unplugged.

 

[Paully's5.0]

put the IAC from my other mustang in place of this one, same deal.

 

[blk92stangg]

It sounds like a VSS problem to me, especially since the VSS is used to keep the car from stalling when coming to a stop, which is your problem.

 

[HISSIN50]

interesting. i would have guessed IAC issue as well (idle probs and falling idle from speed).
i always thought the VSS was necessary, but then Michael posted that he does not have his and he does not have any issues (but then again, he is about 100 leagues above me and his stuff is in tip top shape). i just wanted to toss that out, for further research/thought (that the VSS might not be totally necessary).

good luck.

 

[Rerun]

My speedo doesn't work, not plugged into the tranny. I need to get my lazy ass under the car and put it in there. Nevertheless, because of this I always get a VSS code when I yank my codes. My car dips in idle when I come to a stop but doesn't stall, I'm guessing that my IAC prevents that.

 

[blk92stangg]

Hmmm, I wonder how much Michael's throttle plate is cracked open with the throttle plate screw? I am thinking that Paully's plate is nearly closed, so when he lets off the throttle, little to no air gets into the engine, the VSS is not working, so the IAC doesn't cycle faster to let more in, so it stalls...assuming my harebrained idea is sound, Paully would only need to reset his idle with the throttle cracked open more, so when he does let off the gas, there is sufficient airflow to keep the engine going. Does that make any sense Hissin?

 

[HISSIN50]

Yeah, Blk92, it does. i had posted what i did for Michael to perhaps comment upon (he is the only one who would know). i know other guys and sources have said that the VSS keeps the idle up. i dont notice it on my stang, but i definately do on my eclipse.

oh yeah, i wonder if Michael's chip has anything to do with his situation.

*the only reason i posted about Michael was that i used to post about the VSS being a culprit, but then he posted about his observations a few days ago. i did not want to give bad advice here and now, so i posted what i objectively could.

and we all know no two cars are the same (if they were, there would be ONE cure for idle surging). so butterfly setting, TB brand/design, and chips certainly make a difference.


one more thought for Paully: pull codes. a vac leak (that you asked about) would actually do the opposite - the idle would hang higher. but if your EGR is not working (i dont know in particular what all was removed), and is allowing spent gasses at idle, that would kill the motor.

other than detonation, im not sure of what else happens if the EGR is removed without burning a chip (to let the puter know it is not there and not to advance timing, etc). this was my turn for random thoughts, Blk.

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

A bad VSS will set code 27 or 29