Idle Air Control

[hufhouse]

Can a bad Idle Air Control cause surging during driving, say 35-45 MPH?

The car idles just fine.

[inafogg]

no whats going on

[hufhouse]

1996 Grand Am SE, 4 cyl

The engine surges while going down the road.

I'm also leaning toward something in the front passenger axle and suspension, causing something strange in the CV joint.

[hufhouse]

I've replaced the fuel filter and the fuel pressure regulator, but I still get a feeling of the engine surging while driving...RPMs fluctuating up and down like it's staggering.

However, it seems to be related to travel in the suspension. I notice that the surging seems to happen in relation to the car dropping down...when you feel heavy in the seat. I also hear transaxle noise from the front passenger side at the same time. I get the feeling that there's something that is "disconnecting" when the suspension travels to its lowest point.

So, rather than the engine surge being caused by a fuel problem, I'm thinking the engine may somehow be "disconnecting" from the front passenger tire due to a bad axle or CV joint which causes the engine to race temporarily.

Unfortunately, transaxles and suspensions are a mystery to me.

[inafogg]

your discriptions ''heavy in the seat'' &'' I get the feeling that there's something that is "disconnecting" when the suspension travels to its lowest point''.
need a better discription
have you scanned for codes,checked for vacuum leaks?
what made you change fpr a guess,a dtc,or someone said it might be the proplem
take a look at MAP sensor vacuum hose may have a crack i had this before

[hufhouse]

Well, you were correct on the MAP sensor vacuum hose. It had a tear.

I replaced it, and the engine power increased dramatically. However, I'm still having hesitation problems under load.

Forget about the suspension stuff...it's unrelated. I do think I'm going to need an axle on the passenger side, but that's a separate problem. It's vibrating when the car dips low, which was causing me to think it was related to the hesitation.

Anyway, I'm still stumped by the hesitation after replacing the MAP vacuum hose. It helped, but didn't solve the problem.

I'm also getting P0304, cylinder 4 misfire codes.

I'm starting to wonder if I just need a new spark plug. The plugs were replaced about 10,000 miles ago, though.

[thephantom1492]

wrong spark plug type or gap can cause issues...

mine ask for iridium spark plugs. I read somewhere else that someone put cheap standard plugs in it and didn't lasted 10k miles...

I would pull out the plug and check for wear and all... maybe swap with another cylinder... see if the code move...

[hufhouse]

I was thinking about this overnight.

The broken MAP sensor vacuum hose would make the engine run too rich. It has been doing that for some time now.

I wonder if the plugs are just fouled?

Could be a simple, cheap solution.

[inafogg]

what codes are being read??

[Scrapper]

Originally Posted by hufhouse

I've replaced the fuel filter and the fuel pressure regulator, but I still get a feeling of the engine surging while driving...RPMs fluctuating up and down like it's staggering.

However, it seems to be related to travel in the suspension. I notice that the surging seems to happen in relation to the car dropping down...when you feel heavy in the seat. I also hear transaxle noise from the front passenger side at the same time. I get the feeling that there's something that is "disconnecting" when the suspension travels to its lowest point.

So, rather than the engine surge being caused by a fuel problem, I'm thinking the engine may somehow be "disconnecting" from the front passenger tire due to a bad axle or CV joint which causes the engine to race temporarily.

Unfortunately, transaxles and suspensions are a mystery to me.

have you tried doing a compresion check on this? and it could very well be a axle going into tranny.

[hufhouse]

Only code is P0304, misfire on cylinder four.

No compression check. Truthfully, don't even know how.

[thephantom1492]

as I said, check the plugs, swap them with another cylinder... let's say you swap with 3, if you get a P0303 you know that the prob is the sparkplug.

I doubt the coil is the problem, as it fire on 2 cylinders so you would get 2 codes or a random misfire code.

if you still get P0304 after the swap, I would then check the compression.

[Scrapper]

Originally Posted by hufhouse

Only code is P0304, misfire on cylinder four.

No compression check. Truthfully, don't even know how.

try to rent a guage from autozone you take it back you get your money back or you can try advanced. it theards in like a plug does and guage at the other end.

[Blue Bowtie]

Actually, a failing coil can create weaker spark on one of the plugs in a "wasted spark" system. It depends upon the failure mode of the coil.

[skeeter123]

Are you sure it's not a transmission prob (unrelated to the P0304)? If it's an automatic, it may be having trouble locking into gear. Try running in "3" to keep it from seeking overdrive, see if the surging goes away.
Hope this helps.