4cyl Rough Idle - Brakes Make Engine Stall????

[BoxerPowerBB]

Originally Posted by greenman

Which engine?

How frequently does it occur?

If you haven't cleaned the throttle body lately I'd start there.

It's the 2.4L. It is so intermittent it's hard to stay. Sometimes the car goes months with no issue, then it happens four times in a week. I'm more inclined to think it's some software issue but I will check the TB. Thank you

[greenman]

Originally Posted by BoxerPowerBB

It's the 2.4L. It is so intermittent it's hard to stay. Sometimes the car goes months with no issue, then it happens four times in a week. I'm more inclined to think it's some software issue but I will check the TB. Thank you

You may not like this suggestion but with that low frequency I'd suggest just driving it until its gets worse & pops a code which, odds are, it will. I suspect you may have already heard that.

[BoxerPowerBB]

Originally Posted by greenman

You may not like this suggestion but with that low frequency I'd suggest just driving it until its gets worse & pops a code which, odds are, it will. I suspect you may have already heard that.

Yea either it will be driven till a code pops or traded in lol

[MRC]

I agree with the voltage issue. When my engine is misfiring, the idle lopes all over the place and does dip below 500rpm so that is most likely why the ESC and traction lights are coming on, those systems have nothing to do with the engine running poor.

I do have my cylinder leak down tester so I will try to dig into it today and also checked for a intermittent vacuum leak. The engine breakdown link I posted at the top seems to fit my symptoms.

Also, my car always starts right back up after it stalls, since your's has trouble starting or doesn't start at all, we may have different faults but similar symptoms.

[BoxerPowerBB]

I haven't had time to check the TB yet but my girlfriend came up with a good idea without even knowing what she was saying! She said it would help if my scan tool was plugged in 24hrs and BOOM it hit me lol. I could get one of the less expensive data logging units so that when it happens I've a recorded event of what is going on. Then at least I've got something to go by. That's my last resort other than I don't care if the car spontaneously combusts in the parking lot right now lol

[MRC]

I had time last weekend to do the cylinder leak down test on all four cylinders. Each test showed there was minimal leakage, almost matched the psi added to the cylinder so still in excellent shape at 100K on the engine.

The throttle body is clean and there are only a few vacuum hoses. One from the plenum to the intake and one from the brake booster to the intake. So doubt I have a vacuum leak. And at 100K, my spark plugs were still at factory gap of 0.035" or so.

I do suspect my coil packs though, driving sometimes I feel the car buck or misfire and I believe only a drop out in ignition can cause that sudden jolt, maybe fuel injector but doubt it. Think Rockauto.com had ACDelco coil packs for about $25 each, may buy 4 new ones.

[greenman]

Originally Posted by MRC

I had time last weekend to do the cylinder leak down test on all four cylinders. Each test showed there was minimal leakage, almost matched the psi added to the cylinder so still in excellent shape at 100K on the engine.

The throttle body is clean and there are only a few vacuum hoses. One from the plenum to the intake and one from the brake booster to the intake. So doubt I have a vacuum leak. And at 100K, my spark plugs were still at factory gap of 0.035" or so.

I do suspect my coil packs though, driving sometimes I feel the car buck or misfire and I believe only a drop out in ignition can cause that sudden jolt, maybe fuel injector but doubt it. Think Rockauto.com had ACDelco coil packs for about $25 each, may buy 4 new ones.

You obviously know your way around an engine compartment. The tool you're missing is a diagnostic scan tool which would probably pay for itself with one use. If you have a laptop you can buy a decent software-based tool for around $200. Or maybe you know someone that will loan his to you. Then you'd have evidence you can use to narrow down the diagnosis. Throwing parts at problems is almost always the most expensive approach. Just sayin'.

[MRC]

True greenman. It snowed here recently and my car really started acting up. Lots of random stalling, hiway and at stops, esc and traction errors. I did pull all the module connectors and add dielectic grease for the fretting corrosion tsb, (no help). And I found a thread in an HHR forum about bad grounds which i went through and found minimal voltage drops. Also checked the intake for vacuum leaks with brake clean. Nothing found.

Question: Any of you with a 4cyl get a rough idle and almost stall if you repeatedly press the brake pedal????

I pumped the brakes and rough idle almost stall, clamped off the brake booster vacuum line and pumped the brakes - stable idle with no change. Took the clamp off the line and pumped the brakes - rough idle, almost stall.

That make sense???

[DrivenDaily]

Yeah, it does. Brake booster uses the difference between atmospheric pressure and the lower pressure of the intake manifold to add power to your braking effort. It does this by allowing the manifold to pull air in from the booster. The computer is supposed to detect this and adjust the fuel supplied accordingly. Sounds like yours is missing the opportunity to run right. Good job on testing it and identifying a symptom.

Now, for a real tech person to jump in and offer some truly wise words...

... ahem ... greenman or Rodents ... ?

[greenman]

Originally Posted by MRC

Question: Any of you with a 4cyl get a rough idle and almost stall if you repeatedly press the brake pedal????

I pumped the brakes and rough idle almost stall, clamped off the brake booster vacuum line and pumped the brakes - stable idle with no change. Took the clamp off the line and pumped the brakes - rough idle, almost stall.

That make sense???

That does sound like a leak in the booster.

Try this:
engine running>depress brake pedal
stop engine while keeping pedal depressed
after half a minute the pedal should not have depressed any further
if it did you have a leaky booster