2008 Dodge Avenger Rough/Slow Idle

Hey guys, hoping for some guidance.

I currently live in Savannah, GA trying to help out my fiance who lives in San Diego, CA, so I’m helping from 2,400 miles away. This is my first experience where her car issue is our car issue. Additionally, she is freaking out that this is the first in a string of her car nickel-and-diming her. So here’s the scoop:

2008 Dodge Avenger SXT Sedan
GEMA 2.4L DOHC I4 / 4 speed automatic
75,000 miles
Moderately well taken care of (oil change every 3,000 miles, mostly follows recommended maintenance in owner’s manual)

*Car runs and drives fine while the car is in constant motion and decelerating.
*Rough and Slow Idle at a stop on the brakes with car in Drive. Engine speed will drop below ~400 RPM, then “kick” up to ~1,200 RPM, settle back to ‘normal’ idle ~800 RPM, repeat. I have suggested she put the car in Neutral at a stop to see if that changes anything, but I don’t have feedback from her yet
One instance of seeing a puff of smoke from under the hood while the car was doing the above.
*When pulling away from a stop, the car will hesitate; that is the accelerator will be pressed but the throttle response will be delayed.
*When pulling away from a stop acceleration will be inconsistent; instead of rrrrrRRRRRRRRRR, it’s more like rrrrRRRRrrrrrRRRRrrrrrRRRRR
*Couple instances where the car just shut off while she was parallel parking (low engine speed).
*One instance where the car did not start on first attempt. Started fine on second attempt.
*No Check Engine Light. The codes have been run.

Shop Visits (at an independent garage recommended by her roommate who’s been going there for 5+ years, good reviews on yelp, and always busy):
*First visit: told her they put in a bottle of fuel system cleaner and to use a tank of high octane gas. That didn’t really help.
*Second visit: cleaned the throttle body. That was 3 days ago, so far no conclusion either way.

Other repairs:
*The battery was checked (at O’Reilly) and replaced after the starting incident mentioned above. (5 year old car, seems about right).
*2 nights ago I told her to put in a bottle of HEET to get water out of the fuel system (California uses ethanol blend) and a bottle of Gumout Fuel System Cleaner and to fill up with premium gas (based on items below). Be sure to run that tank down to almost empty.

Things I could think of:
*Crankshaft/camshaft position sensor failing.
*Alternator failing (because this problem doesn’t seem to exist at higher RPM’s)

Research online:
It seems that a number of people have similar problems with Chrysler products with this and the previous generation 2.4L engine but no clear conclusive repair. Some of the items mentioned:
*Idle Air Control (IAC)
*Exhaust Gas Recirculation (EGR) valve
*New sparks plugs and wires. (not replaced but should be)
*New timing belt. Timing belt is one tooth off.
*Water in the Fuel System (hence, HEET)
*Dirty/Clogged Fuel System Component (hence, fuel system cleaner)
*Failing Fuel Pump
*Dirty/Clogged Air Filter (replaced per maintenance manual)
*Low Oil Pressure/Failing Oil Pump
*Additionally, there are no recalls against her VIN.

We’re trying to make this car last as she’s still in grad school and we’re saving to pay for our wedding. She doesn’t know very much about cars and I know a moderate amount. I hate to see her be treated as a dumb girl at an auto repair place, get the runaround from this garage, or get nickel-and-dimed on the repair by throwing parts at the problem.


  1. Has anyone had a similiar issue before? What was the root cause?
  2. What are proposed troubleshooting steps?
  3. I know many auto parts stores will run the codes, anyone have an especially good recommendation?
  4. Taking into account the geographic situation, is it advisable to send her to a Dodge dealer?

Thanks for the help!

There are lots of reasons for idle issues. This one just sounds like a vacuum leak or a wonky idle air control valve (IACV).

Any shop that would tell someone to run a tank of high octane fuel in response to this is not worth the trouble. High octane gas will do nothing at all. The octane of the fuel is irrelevant to this kind of situation. The fuel system cleaner? Maybe, sometimes.

Without any error codes to work from, I would say that a good shop will go over the basics (fuel, air, spark, compression):

  • do a check for vacuum leaks. A vacuum gauge is best for finding out if there is one. It can be in vacuum lines or any other aspect of the intake - manifold gasket and such. (air)
  • the IACV should have been cleaned and checked along with the throttle body cleaning, and the whole intake including air filter inspected (air)
  • Check of the fuel pressure. (fuel)
  • Check of spark plugs, wires, and ignition coil. (spark)
  • with the spark plugs out, check the compression.

Etc electric throughtle control module i just worked on one doing the same thing