Hi,

I have '90 240 with a stubborn rough idle problem. I replaced the injector seals and crank sensor (I had a crank sensor signal missing code) but the trouble remains.

I think the problem is an intake manifold gasket leak. The engine smooths out for a while when I spray carb cleaner under the intake for #3 cylinder. I thought it might be a cracked flame trap to oil separator box hose but I have the oil breather system disconnected and plugged at the metered port and intake snorkel while I do this.

My question is: The Bentley manual says you have to drain the coolant when replacing the intake manifold (or gasket). The FAQ for this site doesn't say to do that. Do I really need to drain the coolant? Just put new coolant in.

Any other advice would be welcome.

Thanks,

Mark
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' 93 240 (Quinn), AW70, 130K. '90 240 (Amanual), M47II, 97K. '92 240 (Edgar), AW70, 170K, totalled parts car. Love to drive them when my kids let me!

Carbureted 240's have an open passage to the intake manifold to heat it. The fuel injected models have plugs in the head block this passageway.

No need to drain coolant in the B230F: just remove the manifold. The 700/900 FAQ instructions apply to your car.
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See the 700/900 FAQ at the select shortcut button on the top right of the screen.