Pizza's Turn
 

Ok, it finally happened, I am faced with something I have never seen before. Now, we are all familiar with the stories of the lady in a minivan (why is it always a minivan?) who can't stop her van from accelerating, right?

Yesterday, after having rear tires put on (went with Hanooks in Gary and Kim's wider version, again), I drove to the mountains to walk. On two curves, it SEEMED like the car was "dizzy" or sliding. What the hell is this? But later, it would occur to me what was going on...


I had left the car parked for ten minutes when I started it and headed down hill in TIGHT curves. It SEEMED like it was accelerating at times. I THOUGHT I had hit the cruise lever by mistake. So, the second time I felt it, I pushed the clutch in - the tach went to 4K and sat there about 5 seconds and then went to idle. The next time it went to 4K I tapped the pedal and it settled to idle. It kept doing this over and over - one time, with the clutch in, it went past 4 to 5 and I turned the key off! Turning the key on and letting the clutch out, of course, started the engine and I was down the hill. I was about out of gas, so I filled it up at the station at the bottom of the hill. All ok all the way home (about 40 miles). I'm thinking the throttle position sensor at the pedal is at fault.

It was not until I got home that it occurred to me -DUH!!!! I can set the Ultragauge to display the throttle position the ECM is getting - if it rises during these times, I know it's the TPI. But if it doesn't, then it goes back to the ECM, I guess?


I don't remember ANYONE ever experiencing this - am I right? Did I just encounter a new (to us on the forum, anyway) problem? Anyway, the Ultragauge is set to display throttle position percent... we'll see.

Oh, and I have no CEL, no codes and no pending codes - per the Ultragauge.

Re: Pizza's Turn
 

The accelerator pedal rheostat(s) tells the ECM what you want to do.
The ECM makes the TB stepping motor run.
The TB tells the ECM where it is via the TPI rheostat.
The ECM tells the UG what it is seeing from the TB.
( I would call it more drive by committee, than drive by wire )

I am not really sure if the ECM runs the stepping motor in reverse to decrease throttle, or depends on the honkin big spring in the TB to do that.

The Ultra Gauge has no idea what the gas pedal is doing.

If you suspect the TPI in the TB, you can remove the plastic cover on it and clean up the contacts and circuit board resistor runs.

Re: Pizza's Turn
 

Yea, I already figured that the indication was NOT of the pedal position.

But I had not figured out the REST of it - thanks, I'm still watching it, I drove about 80 miles today - no problem.

Kinda wondering how long I go before it does it again....

Re: Pizza's Turn
 

I'm going back to the rheostat in the pedal - because I don't see how the engine made more power just due to the TB opening up - with more air but not more fuel from the injectors.

AND.... if the TB and the injectors worked together to make more power, the ECM told them to.

Why would the ECM do that if the pedal rheostat didn't command it?








But even so... something tells me I'm still not right.......

Re: Pizza's Turn
 

Insubordination, I guess.

Re: Pizza's Turn
 

In any event, it has not done it again - not since throwing two fits on Friday.

Re: Pizza's Turn
 

Got that beer bottle off the floor.... :p it must have been pressing on the pedal... LOL

Re: Pizza's Turn
 

Re: Pizza's Turn
 

No, it did it at least SIX times in the three miles down the hill !!!!!!!!

I thought that at first, but it just kept doing it OVER AND OVER.... then I get to the bottom of the hill and drive about 3 miles more to the gas station and it did NOT do it at all! I'ts almost like it didn't like the steep downgrade, but I've driven that road about 20 times in the past two years and it never did it before.

Re: Pizza's Turn
 

Check your vacuum lines.

Re: Pizza's Turn
 

Will do! I REALLY need to understand the whole system better.

But will do....

Re: Pizza's Turn
 

Could also be an RCM issue. Might be worth it to check that out as well. I'm certain mine is bad so I'll be getting a soldering iron soon.

Re: Pizza's Turn
 

Mark, I was at a test and tune day local track some time ago and experience throttle pedal problems. It seemed all those stomping on the throttle runs had loosened the whole pedal assembly. The floor mat had pushed up against the throttle pedal unhinging it a bit and it was all but loose. Throttle felt normal but wasn't in the right position. At least get down there and take a good look...:cool:

Re: Pizza's Turn
 

You actually might have something there DOc. I had a similar issue years back. It turned out to be a fold in the floor mat moving the pedal.
Completely forgot about it till I read your post.

Re: Pizza's Turn
 

Hmmm.... this would make a lot of sense.... running into the garage!

Re: Pizza's Turn
 

That was a dead-end, quite sure of it.

My mats are kinda narrow and are not interfering at all. I REALLY have the gut feeling that the sensor at the top of the pedal is bad.
I remember that, this past winter, when the car was below 40F, as you pressed the pedal, it would "snap", once the car warmed up, it would not do it. Did it every cold morning, and even on cold days on the way home from the office.

I know, that proves nothing, but still... I'm going to price a new sensor for the pedal and just keep waiting for it to act up!

But i'll still look over vacuum hoses and lines.

Re: Pizza's Turn
 

There's 3 tubes you want to look at, they are in the back of the engine and connect to the MAF housing which connects to the throttle body. I've had two of them leak and cause issues. Whenever I would go out of gear into neutral the rpms would shoot up then go down to idle after about 5 seconds. only cost me $2 for a foot of hose. Cheapest car fix ever.

Re: Pizza's Turn
 

I'm on it, thanks!

Re: Pizza's Turn
 

Probably the first time you were thankful to not have a SRT.. sounds like the clutch really helped you out there

Re: Pizza's Turn
 

Mark I was experiencing the same issue the last time I went to the Dragon, after I installed the 74mm TB.

The RPMs would go from sub 1,000 to nearly 4K and then back, over and over again like someone was revving the car. I never did figure out what happened, and I tore the entire intake/TB system apart several times with no changes. After I drove it a few hundred miles, it just started working properly and I have not had an issue since.

I was hoping mine was simply trying to adjust to having more air, but who knows. Have you changed anything recently? Added a CAI, TB, catch can?