Just picked up an 040 190d this morning. When starting, the glow plug light went off right away. Im assuming this is cuz of a bad glow plug relay. Would this be a good diagnosis? Any way to test it?

Anyways i let it sit for 5 mins in accessory mode hoping it would heat the plugs even though the dash light was off. After 5 mins i tried to start it and it just cranked and cranked. Then i turned it off and let the glow plug heat again for about 30 secs and it started to sputter. I gave it some gas and it slowly came to life running rather rough. After keeping the gas on it for about a minute, it held its idle.

I took it for a spin and noticed that when i let off the gas it made kind of a sucking in/compression sound that is definitely not normal. I was wondering if that is a symptom of a cylinder not firing and just making compression due to a bad glow plug. Does that sound about right?

Anyways if you agree with me, im going to order a new set of glow plugs and relay. If not, let me know what you think it could be! Thanks

__________________
1993 2.6 (040) SportLinE 5-speed - Armed to the teeth w. roof rack/2x bike carriers/8x ski carriers/MB towing bumper
1993 2.6 (040) - deceased/reincarnated as a trailer.
1987 16v (702) - Now parting out(9/22/10)!!! - Email me your requests for 16v parts- Engine and full body kit avail!!
1987 300SDL (122)- For sale!