SOURCE: 1999 saturn sl1
Sounds like you have one of two problems. If the car has over 80,000 miles on the odometer, your idle air control motor (basically an electrical solenoid valve which allows additional air into the motor past the closed throttle valve) is sticking open.
The other possibility is a vacuum leak. I would try removing the IAC (idle air control motor) and cleaning it using aerosol carb or throttle body cleaner. This is available at any auto parts store. Re-install the valve and see if there is an improvement. If it improves but reverts to it's old behavior (usually within a day to a week) you will need to replace the valve.
Charlie
SOURCE: 1999 passat tdi power fault
Air mass sensor, almost never shows codes but always makes the vehicle loose power !! cheaper from vw than pattern and more reliable
SOURCE: Engine vibrates, shakes car at 1700 rpm, smooth at 2000 rpm
Something similar happened to my van, and it ended up being that I needed to replace a tie rod in one of my wheels. Hope this helps! I know this was posted awhile ago.
SOURCE: 2000 Discover TD5 Auto harsh vibration under power at 2000 -2500
The "lift off and it goes away" is the clue I feel. This eliminates engine out of balance issues and points squarely to fueling issues. I would say try a compression test (always a good first start before you try much else) but with plenty of power and no vibration except in the range, probably not a compression issue. So, what's left? Fuel or air is the answer. Check air inlet path is from air filter to turbo and (more importantly) from turbo to intake manifold. Check wastegate on turbo is OK - disconnect the wastegate (it's bolted on to the turbo) hose, then **** on the wastegate hose, you should feel resistance. If not wastegate aneroid has perforated. At this point, I suggest taking it to a LR dealer and get them to pull all the engine codes. If all OK, next step is injectors. It's a common rail diesel and removal is a bit tricky, but if you pull them out, you will often be able to see a single injector with all the carbon deposits around it. If all injectors look the same, suggest that at this point you need to take them to a diesel specialist for testing and calibrating. This process usually cures 70% of diesel misfire problems. The other 30% really requires specialist knowledge of your vehicle's engine.
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