I recently purchased a '99 turbodiesel and have a question about start up.
I turn the key and when the engine starts it runs at about 1200 rpm and will continue to run at this rpm until I bump the accelerator pedal a couple of times and then it will go down to 600 rpm.
I'm just wondering if this is normal and I should also mention there are one or more glow plugs that are bad.

Normal if the glow plugs are bad. The ECU is trying to compensate for the misfiring cylinders and prevent it from stumbling and possibly stalling and warm up faster. Let it do that for about 2 min and let the idle back so it doesn't smoke as much

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Does not sound normal behaviour to me, my 97 has had 3 dead glow plugs and would start and fumble and shake but never raised the revs up.

I would check the pedal angle sensor. With the engine off, have someone push the pedal and make sure the spool travels freely.

Or get one of those cheap OBDII data transmitters and an Android device. Even a cheap dollar store tablet will work if you don't have an Android phone. Go to the Play Store and find the "torque" app, and connect it to the transmitter. Place the widget for the throttle angle sensor on screen, and check that it goes from 0 to 100 reliably as the pedal is pressed and released. You'll have to have the key in position II to get the OBDII to transmit but you don't want the engine running for this test.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

There was updates between 97-99. I wouldn't be concerned about this. Mine did it RIGHT after the glow plugs became an issue... My other 98 did this as well prior to me replacing the glow plugs and after replacement I disconnected and reconnected the negative terminal and all problems went away with new plugs.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k