Hello! Everyone. I got a 1991 Mercedes 190e 2.3L, which has a hard start problem when the engine is warm.

Cold start is ok, take about 4 cranks on the starter to start the car. After shut off and start immediately. It can start right away. But when park the car about 2 hours, then feel hard start the car (take about 8 to 10 cranks).

I already put new Bosch injectors, new bosch accumlator, new Bosch fuel pressure regaulator, hengst fuel filter, new battery and new Bosch oxygen sensor. Still the same problem.

Also, put 3 different used ovp relays and used CIS water sensor ( from my past parts car) . Still same problem.

Anyone has an ideas what problem.

Have you checked the fuel pressure? This would be a good place to start to make sure you have enough residual fuel pressure for a warm start. The fuel pump check valve may be faulty.

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1989 300CE

I don't think so that is fuel pump check valve problem because i replaced a brand new Bosch fuel pump about 2 years ago. I parked the car over a year. Before park the car, it can start anytime perfect.

Yesterday, I refill the premium chervon gas in that car. Since improved on starting. At least, I can feel that little easy on starting. I will keep update in next few days. Hopefully, it causes by poor quality gas. Not something wrong on the car.

Did you put fuel stabilizer in the tank when you stored the car?

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1989 300CE

No, I didn't put fuel stabilizer.

I would bet that the fuel is old and stale. I would run a good quality fuel system cleaner and put some fresh fuel in the car as soon as possible.

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1989 300CE

Updated!

I finally found out what problem cause hard starting

The throttle body return spring is broken, which causes the throttle body not close enough. The spring is hide under the air flow meter.

2 days ago, took off the air flow meter and clean the throttle body... then, discovered the broken spring.

After put the new one on, all become normal.

Thanks for posting your solution. I also have hard warm start and have replaced injectors and accumulator.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K