Car stalls when letting off the gas

[cymbalrush]

Hi guys,

Hope you all don't mind me coming here to ask a question. I drive a 1994 Cadillac Seville with about 160k miles on it, and it's been a really, really great car -- except for the past couple of weeks, where it's been stalling pretty consistently.

The car idles fine, though at a much lower RPM setting than I've ever noticed, but when I'm driving if I take my foot off the gas for even a second, the RPMs tank and the car stalls. It'll start right back up if I throw it into neutral, but it's still a very annoying and inconvenient problem to deal with, especially because I have to two-foot drive and I'm pretty worried about doing something to my brakes or boiling the fluid.

It also doesn't behave this way all the time; I can tell when it's ready to stall because the gas pedal loses a lot of its pressure and it's very "squishy." Normally it has a good deal of resistance, so it's easy for me to know if it's safe for me to let off the gas for whatever reason.

Here's what's already been done in response to the problem:

- New fuel pump
- New fuel filter
- Cleaned throttle body
- New throttle position sensor
- Battery leads cleaned/tightened

Not so much as an improvement from any of these. At this point, my mechanic is convinced it's electrical, but I'm not so sure -- as I don't think an electrical problem would affect the resistance of the gas pedal or allow my car to alternate between modes of "working" and "prone to stalling."

Really, any sort of suggestion or advice at this point would be greatly appreciated -- I'm a broke college student, so I rely on this car heavily and lately it's been the cause of a great deal of stress.

Thanks a lot!

 

[master_shake_]

is the egr valve stuck open?

does it run rough then bog out or just bog out and die?

 

[cymbalrush]

is the egr valve stuck open?

does it run rough then bog out or just bog out and die?

I haven't checked the valve. If it were stuck open, would that be something I could feel while driving? If so, it's most likely not that -- the car drives like a dream while it's actually working (which makes it even more frustrating that it has this problem)

And it just dies. Doesn't run rough; I let off the gas and within a second the RPMs have plummeted and the car's stalled. Sometimes it's so fast I don't even have time to curse myself for forgetting to keep my foot on the gas.

 

[phucheneh]

If you are 100% sure that the gas pedal thing is not all in your head...it's probably gas pedal, throttle cable, or throttle body related. 'Intermittently feels squishy' is just...a bit of an odd complaint.

I mean no offense by mentioning that your mind might be playing tricks on you- it happens with automotive symptoms. And I'm also going to mention something else a little silly...I have seen both 'surging' complaints from a floor mat sitting on a gas pedal, and 'lack of power' from a mat underneath it. It happens. If it turns out to be something simple, don't feel bad, just be grateful it was that easy.

That said, the first thing I would so is start at the throttle body. Open and close it using the bracket on the side. Try it with the car off first, and see if you feel any binding or sticking. If there's an adjustable stop, look for signs of it being moved (it generally shouldn't be). Start the car up and see if you can replicate the issue at the throttle. Does barely nudging it open keep the car running? But it immediately dies if you let pressure off?

Northstar engines are pretty alien to me. I'm not a GM guy and I'm too young to have worked on that car when it was newer...and to be completely honest...it's the kind of thing I try and avoid. Around here, most of those cars end up in the hands of those that do not maintain them, and doing drivability work on them is opening a big can of worms. So I'm guessing here. Some GM guys may chime in, but I'd advise that you hunt for some info on a Caddy forum. You might not get the BEST info, but it'll probably be a step in the right direction.

If this is an electrical issue, it's likely either a throttle position sensor (out of adjustment of just 'bad') or an idle air control motor. Plugged up IAC would be my bet.

Does it have a check engine light?

 

[tortillasoup]

Yeah plugged up IAC could be the cause. OP should clean the IAC, disconnect the battery and try driving the vehicle again. If OP already cleaned the IAC (Idle Air control valve) and is NOW experiencing this issue, it's possible OP forgot to disconnect the battery to reset the computer as the computer "learned" to operate with a dirty throttlebody/Idle Air Control valve.

 

[boomerang]

First thing you do is find another mechanic. That's not a mechanic you're dealing with that's just a guy that knows how to turn wrenches and he's costing you a lot of money. If he did all that work for free including the parts stick with him. If not, it's time to move on. Anybody that throws that many parts at a problem does not know what they are doing.

I'm wondering if the torque converter clutch is not unlocking. I was also wondering if this car still used a manual kickdown cable for the transmission but I think the car is too new for that. If it did, that could explain the different feel you get from the gas pedal along with the stalling problem. The IAC is a great suggestion but any mechanic worth his salt would have checked that especially when supposedly cleaning the throttle body. In fact to clean the throttle body properly, any mechanic worth his salt would have removed the IAC. I still would investigate that.

The different feel from the accelerator pedal is the key to fixing this problem. Take a close look at any cables related to the cruise control.

 

[Meghan54]

Agree the IAC is probably the issue. I'd just go ahead and replace the thing given the year. Rock Auto has a Standard IAC for the car for $48. But you're right, tortilla, he needs to disconnect the battery when replacing it and then reconnect so the computer relearns.

 

[tortillasoup]

Well the way I look at it, by cleaning the IAC, save time and money since you don't have to wait for the part to arrive. These IAC rarely go bad and it's usually just gunk that needs to be cleaned up with a q-tip and rubbing alcohol/carburetor cleaner. If I can get something done sooner by just cleaning the part, I'd rather just clean the damn part then spend money on a part that is no guarantee that will fix the issue.