Idle Problems

[nuQ]

just to get this out of the way first, i'll be doing a cpu diagnostic on sun., and i've read through the old posts..........

since i've owned the Q (since feb.), it always had a slight "snort", bucking thing while at around 40 mph thru 65-70 at a steady speed. had a complete rail clean, fogger, done about 2 months ago. in the last week the "bucking thing" at around 40 seemed to be getting slightly worse and tonight, while the engine was warm, the idle started to jump in park and drive. would go from 600 rpm (normal) up to 1000 down to 100-200, almost die, then back up to 1000 then back again. looking through the old posts, the MAF connection seems to be a major first step. could the EGR valve be something too??? just looking for a pre-heads up before i dig in. anyone have a similiar experiance with the Q, which is a 90????? thanks as always, jeff

[Q451990]

Bucking sounds like knock sensors to me. Idle hunting is probably intake dirt or something related to an electrical connection (MAF, CAS, etc.) I wouldn't think EGR function would have anything to do with the idle hunting since it's not open at those RPMs. Could have some impact on the cruise bucking though.

Heath

[Q45tech]

The usual failure mode for EGR is none [emission NOX failure] or not enough [partial clog in passages]. Therfore if you feel it at all it might show up as transistional tip in acceleration pinging in Summer at low speeds in top gears [lugging].............sudden acceleration but not fast/strong enough to down shift.

We have seen a few MAF failures of late [on 10-13 year old units]...they become microphonic [sensitive to vibration/tapping lightly]..........may not throw a code ......study the MAF voltages at idle [1.2 volts] but remember as the rpm drops so does the MAF voltage.

We usually just substitute another good MAF and see if the problem goes away since........the diagnostic takes longer and is more complicated than the swapping.

[nuQ]

i'll be using a voltmeter tomorrow, never used one before,,,what is the procedure to test the MAF. assuming that it should be check when the engine is cold to see if the reading is 1.2 volts????? any advice would be helpful!! thanks jeff

[Q45tech]

Just remember you are dealing with a sensitive $500 device [the MAF].

We never use a voltmeter to read the MAF as most will load the voltage down, we read what the ecu says it is receiving from MAF via Consult. Follow you FSM proceedures closely!

[nuQ]

can i do that from the Q's computer LED single light????????

jeff

[DAEDALUS]

No. Either use a voltmeter or have a dealer do it with a Consult interface. You can get a voltage reading at the MAF itself, or from the ECU with a (very) carefully placed thin wire from the DVM. The MAF is easier to get to, but honestly I've only measured it from the ECU.

[Q45tech]

Cheap VOM have high circuit loading make sure the sensitivity is rated at 10,000 ohms per volt or higher!

The problem is that most MAF show good voltage readings and without a digital storage oscilloscope you will never see minute variances or time drop outs in the voltage at idle.

The idle air flow is something around 6 grams per second at 1.20 volts and 180-200 grams per second at 4.44 volts.

After the engine has warmed for 12-15 minutes and idle rpm is perfectly steady [+-20 rpm a 675] - Wiggle the connector, tap the unit lightly while watching the VOM.........don't push down on the top rectangular cover plate as too much can force a metal shield inside in contact with components causing a short and destruction of the MAF!

Really is so much easier to swap MAF [5 just sold on ebay for around $30-40 each delivered].

[nuQ]

JUST WANTED TO GIVE A BIG THANK YOU TO DENNIS, HEATH AND DAEDALUS!!!!! went out today and removed and cleaned the electrical connection to the MAF, removed the intake hose and cleaned inside the MAF, and cleaned out the throttle body. she started right up, warmed up fine, then took the same drive i did fri. night when the idle was jumping. ran like a million bucks!!!! what a great feeling. it's almost theraputic (at least for me) to maintain, diagnose, and fix the Q. getting her out on the road and feeling the thrust makes it all worthwhile!!!!! thanks again, jeffps-in many ways you guys are soo much better than the service manual. i looked up unstable idle (the closest to my condition) in the manual-EC70, nothing about the MAF. i would have been going through many other procedures, and wasting tons of time,,,and money!!

[Q451990]

Glad it worked! There are very few things that give me the satisfaction of fixing something on the Q and taking that test drive where everything just seems right with the world again!

Heath