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[Help] Rough idle at stop lights and rough ride at low velocites (1st gear)

I have a 2002 Volvo S40 with 98k miles on it. Recently I have been experiencing rough idle once in a while while stopped at a red light and rough ride at low velocities, plus sometimes slugish acceleration.

The symptoms are as follows:
The car will stable idle for 10 seconds or so and then every 10 seconds it will just hickup (low rev and back to normal), it happens every 10 or so seconds.
Then while I press on the accelerator the car runs fine but sometimes it will hickup while accelerating (like skip a beat).
At high velocities (highway speeds) the car runs fine.

I have done the following things to it so far:
1) Changed the oil (fresh M1)
2) Changed the Engine Cold Air Filter
3) Cleaned the MAF with a MAF spray
4) Cleaned the Throttle Body
5) Reset the computer so it can re-learn the new trims.

No real change.


Also the car sputters when traveling in reverse.

Cho Baka
Check for a loose air intake hose.


reply to roughidleboo
Um spark plugs? Ever do them? lol.

You running 93 in it? Turbo she likes high test...

Really needs to be hooked to a scanner see what the car is seeing.


Ran a free scan from autozone. No codes.
Was thinking about sparplugs or coils, but no misfire codes are thrown.


Grenada, MS
reply to roughidleboo
My wife's 2001 v70 does the same thing. Try turning off the A/C and see if it changes. My wife's car only does it when the A/C is on.

Also it could be the MAF sensor could be going out. Had it happen to my wife's 98 s70 she once owned.


reply to roughildeboo
Not codes, live data... I had a 00 nice car but everything on it is a computer.

To diagnose the issue (not just throw maybe parts at it) you really need to watch the live data and see what changes when the cars idle drops. Sadly for free... likely not going to happen.

Doing what Cho Baka See Profile said is a good plan checking for vacuum leaks is time but free.

Could be a IAC motor, TPS, plugs (I suggested plugs because that is normal maintenance)

Not suggesting anything this site says but I copy and pasted for this reason

"The hard-to-diagnose misfires are the ones that come and go and don't set any codes. These are the ghosts that can drive you nuts."

Again not saying you have a miss just saying node code does not = no miss. All no code means is all the conditions for setting the misfire code were not met.

reply to roughidleboo
Sounds like a very annoying problem. Probably easily fixed once the cause is identified. Unfortunately unless you luck out so to speak the most realistic way is to have it checked or diagnosed professionally. For instance have it hooked up to a scope. Or simply having a qualified mechanic look around and they might even visually find the problem such as an airflow or vaccuum problem.

Good luck!


Cordova, TN
reply to roughidleboo
If this only occurs with the A/C on, then suspect an idle air control problem (something else may just need cleaning). If it's not related to the A/C, then suspect a vacuum leak somewhere. These are often hard to find but easy to fix temporarily with a bit of tape or similar. Behavior like this can also be caused by moisture in the fuel tank or by misbehaving fuel injectors, so it would't hurt to buy a bottle of quality fuel injector cleaner, put it in the gas tank, and give it some time to work.

Jim Gurd
Livonia, MI
said by scross:

moisture in the fuel tank

Highly unlikely these days with fuel containing 10% ethanol. The ethanol would absorb any moisture which might be present and allow it to be burned up.


Cordova, TN
True, in general, but as this water passes into the cylinders it may still cause poor ignition. The alcohol helps dissolve and disperse the water, so the engine doesn't just outright die on you, but there may still be some noticeable effects from the moisture.

BTW, "10% ethanol" just means "UP TO 10% ethanol, but no more than that". At any given moment, a batch of gasoline may contain anywhere between 0% and 10% ethanol, so if you suspect a water contamination problem then you might still need to add a bottle of water remover to your tank.

Also, I forgot to mention that this is the time of year when gas stations in urban areas which are operating under EPA restrictions start switching from cold-weather gasoline to warm-weather gasoline, which is formulated differently and may cause engines which have minor operating issues to run more roughly. In fact, in my experience ALL engines will generally idle more roughly.


Douglasville, GA
reply to roughidleboo
Had a similar problem a few years back with a pontic grand am I owned. It had a bad manifold gasket....