2001, 2.4L-Car shudders, Hestitation from Stop

[carbon02]

Working on my stepmothers 2.4L Alero 70,000 miles. Car starts and runs smoothly, but when you accelerate lightly from a stopsign there is no issue, when accelerating harder the car shudders and shakes like going over a wash board.

Seems to occur only from a stopped position when taking off. Doesn't occur with the car moving.

No codes stored. I've got a copy of the scantool datastream, and it looked like the IAT sensor was slow to respond to changes and it showed a momentary quick drop in temperature to nearly 0F, so I replaced it. Car shuddering still occurs.

Car at idle is running approximately 12-15% load as reported on the scantool. This seems high, but might be non related. I'm not sure how PCM's calculate load.

Short term fuel trim is -8% to 5% so I'm assuming that O2 sensor might be ok.

Car has approximately 70,000 miles. Is this a transmission issue? Any idea's from the 2.4L guys out there?

I still can't figure out how the 2.4L monitors airflow without a MAF sensor, I guess I just haven't studied this engine that much, as the car's not mine and I'm not aware of all the "quirks" of this engine family.

I'm typically over on the Intrigue Forum with the 3.5L shortstar, but it looks like this forum's fairly active.

Thanks

[undersc0re]

Is it doing it under load at lower rpm, heavy throttle at higher rpm? Give just a few more hints and maybe I can give you some ideas.

[carbon02]

Yes it seems to happen when taking off from a stopsign at fairly good throttle. I can't remember the exact RPM's but I'm thinking 1800 to 2300-2500 rpm. I mean you don't have to hot rod stop on it to get it to happen, but if you accelerate quickly under high RPM and a mid throttle it occurs. This would be similar to getting on a freeway entrance ramp. It is intermittent, sometimes it occurs and sometimes it doesn't, but it always occurs when taking off from a stop sign. Once it's going heavier throttle doesn't seem to cause problems.

Forgot to mention it's the automatic transmission not the manual one
Thanks for the thoughts--

[undersc0re]

I would first suspect tranny and its servo's. Maybe try it with the shift lever in first or second and see if it does it. Does it do it when its hot and cold? Check fluid in tranny and have a quick listen for vacuum leaks. Make sure she didn't drive over sumthin on the road and knock off a wire or sumthin at the tranny etc...

[undersc0re]

I know I had a problem with my 2.4 alero, I would hit the gas at lower rpm and it would missfire and hesitate, but when I got up to higher rpm it was less noticable. Easier to test this on my manual tranny though. It ended up being a spark issue, it would leak through coil housing under load, replaced housing and plugs while they were at it and all was good, I also had similar problems with a bad tank of gas I got at the local convienience store, cleared up after I ran a good tank of gas through.

[chopsdogg]

My girlfriend is having the same exact problem you describe in a 2004 3.4L V6 Alero, 100k miles.

I notice it when she does a rolling stop at a stop sign and then hits the accelerator kind of hard. We have had it happen a few times when at highway speed and then get on the accelerator to pass. The RPMs shoot up to almost 3000, but there is no power being transferred to the wheels. If you let off the accelerator for a second, let the RPMs drop, then get back on slowly the problem goes away. This happens when the vehicle is hot or cold, doesn't matter.

My first thought was low tran fluid, but the system is sealed and you cannot even check the fluid levels...lame.

She also has the ABS, Trac Off and Service Vehicle Soon lights on, but they have been on for well over 2 years before this problem. The ABS, Trac Off and Service Vehicle Soon lights on is a rotation/position sensor in the hub assembly. Could be related, but not sure.

I have spark plug wires and fuel filter ready to replace, and going to do this in the next week or so. If that doesn't work going to replace the hub assemblies next although that hasn't been a problem in the past except for the loss of ABS.

Would love to hear any other ideas!

[cooter2]

I had a '99 with a 2.4 that would hesitate and stutter when accelerating from a stop. and a couple times it died when cruising and then coming to a stop. However when driving it normally it ran great. It also always started right up.

The problem: bad vacuum line. It was going into the throttle body. check your vacuum lines first, it is easy and cheap.

[chopsdogg]

My problem went away after replacing the right front hub assembly. Easy job and like $120 for the part new. If you look in the owner manual under ETS, it tells you that if ETS is on and the sensor detects either of your front wheels spinning or slipping that you can lose engine power and possibly shift to regain traction. The Low Trac light will also come on. Although if you have the 3 lights on because of a bad hub assembly, you will not see the Low Trac light. It makes sense if the sensor is broken that the system is detecting some spinning or slippage and causing ETS to kick in.

You could try to just turn off ETS and see if your problem goes away.

Also a tip to figure out which hub is bad, just jack up the vehicle and plug the new hub in to each side and turn the car on and see if the lights turn off. If they don’t’ turn off, try the other side. If neither turns off the light, they are both bad. I guessed the right one on the first try, because I was hearing noise from the right side from the bearings going bad as well.

[mike leuters]

I am having this same problem. Check engine light is on with a cylinder 1 misfire code. While diagnosing i sprayed Throttle body cleaner on the intake next to the 1st cylinder and the engine smoothed out i will be replacing the intake gasket

[dnd02alero]

in response to post #6, I have the same problem with my 2002 3.4L, did you figure out what was causing it?

[cooter2]

My alero had a hesitation and would sometimes died when stopped or just starting, but was fine when normal driving.

It was a vaccuum leak.....