4kq acceleration issue
syljay at optonline.net
Tue Feb 13 14:25:58 EST 2007
Adding to Ben's list of probable causes.
Fuel Injector seals
Testing: bendable copper tubing attached to hose which is attached to
With engine idling, move the copper tube in and around all vacuum leak
sources, including in and around the injectors. When you hit the leak, the
idle will change.
Injector seals are rubber O-rings. These can and do dry out, become brittle
over time and result in leaks . .sometimes only under cold/hot conditions.
OK when hot, leak when cold.
Another method of detecting the leak is to watch the O2 sensor voltage.
Disconnect the oxygen sensor from the harness. The engine is now running on
mechanical fuel mixture inputs only.
Also disconnect the DFP connector so the computer cannot correct the
Use a sensitive DVM on the disconnected oxygen sensor lead.
Use propane as outlined above to do the leak testing. When you hit a leak,
the O2 sensor reading will change along with a change in idle speed.
High Idle, intermittant:
Sticking throttle body plates. This area gets gummed up over time, and the
plates will stick. If its warm, plates will close. If its cold, the gummy
sludge wont be soft enough to give and the plates wont close.
Remove throttle body and clean thoroughly. Put in new gasket when replacing.
O2 Sensor test:
With engine warmed up:
Pull back insulator from O2 sensor connector.
Voltage will be swinging back and forth centered around 0.7 volts if the
sensor is OK.
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q
> From: "Ben Swann" <benswann at comcast.net>
> Subject: 4kq acceleration issue
> To: <armodis.list at gmail.com>
> Cc: quattro at audifans.com, 'Ben Swann' <benswann at comcast.net>
> Message-ID: <079401c74f79$4f6e8a30$7001a8c0 at swansong>
> Content-Type: text/plain; charset="us-ascii"
> Here are things to do and try - seems the car needs some sorting due to
> neglect. Once you get it sorted, it will be sweet.
> - The valve cover leaks and the lifters clack pretty bad.
> *** Well - seems like you need to replace valve cover gasket. If you
> lifters then do the gasket at that time. Lifters are source of clacking.
> Running higher/extended viscosity range ie. 20W50 may help - I like
> GTX or even better Syntec 5W50. Fix your leak before spending the money
> Syntec. Try tightening the cover nuts uniformely to see if it helps with
> leak - don't overtighten. Try running good quality oil before getting
> lifter replacement - these engines like higher viscosity oil again
> 20W50 (or 10W40 if in cold climate) or 5W50 synthetic and you can run it
> - It idles high, usually a little above 1000.
> *** Couple probable causes include: vacuum leaks; Idle stabilizer valve or
> circuit - likely culprit is the idle switch - check/repair/replace - they
> go bad over time; Replace vacuum lines. You'll likely find some obvious
> culprits. A lot of folks immediately assume ISV is bad - more likely it
> the idle switch and/or throttle body screw o-ring. Try jumpering the idle
> switch connector and see if the idle drops.
> - It has some trouble starting in the cold. The colder it is, the harder
> is to start.
> *** As above - vacuum leaks likely culprit. Also Injector seals. Might
> Fuel Injection Thermo Sender, but do the other repairs first.
> - I have to give it some gas to get it to idle steady but then its good to
> *** As above - air leaks.
> - Sometimes it will almost stall until I get the car moving and then it's
> *** Air leaks!
> - The temperature gauge usually sits between the 1/2 to 3/4 mark unless I
> the heater on and then it drops down to between 1/4 and 1/2.
> *** Normal
> - The motor diesels.
> *** Running too lean - air leaks. Possible other cause, but fix most
> causes first.
> *** You need to spend a good day sorting it out. Be equipped with about
> of good quality vaccum line and some rubber hose bandage tape to repair
> OEM hoses that may not be readily available. Replace the Air Filter and
> out all the garbage. Clean up the throttle plate area too while you are
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