190E odd startup behaviour

[Orchid87]

Hi,

New poster here so apologies if i'm posting in the wrong section.

Over a month ago I took ownership of a 1992 Mercedes 190E 1.8 with 64k miles on the clock. She's been well looked after and garaged her whole life.

Everything has been fine except she has odd startup behaviour and i'm trying to pin down what it may be if anyone has any ideas?

Below is some examples of what happens upon ignition;

Scenario 1 - Cold engine after sitting for a week

Engine fires up fine with revs hitting around the 1000 mark then suddenly drop to around 500 rpm before immediately jumping back up to around 900-1000 rpm and idles fine.

Scenario 2 - Hot engine after driving about 65 miles on a mixture of motorway and city streets in hot weather

Engine fires up fine again with RPM hitting around 900 then it drops to 500 and the car shakes a little whilst RPM recovers to 900 again.

Scenario 3 - Same day as above, about 5 hours later.

Pretty much same as scenario 2.

Scenario 4 - Cold engine after sitting overnight.

Pretty much same as scenario 1.

Scenario 4 - Same day as above, about 20 mins later.

Engine fires up really quickly, almost as if it's tripping over itself it wants to start up so quickly but again shakes a little whilst it recovers from it's drop to 600 RPM.

Car has new fuel pump and filter as it was buzzing loudly when I got it. Distributor cap and leads replaced in 2004 and the car runs totally fine otherwise it's just the ignition behaviour that's a bit odd.

Anyone have any ideas? I thought it might be some fuel sitting on the cylinder or in the system which causes the shaking if I start it too soon after driving last but not sure if this explains the drop in RPM at each start before recovery?

I'm not hugely technically minded and any research i've done suggests it may just be a faulty IAC valve but again not sure this would explain the symptoms only occurring after the car has sat for around a week.

 

[Orchid87]

Anyone?

 

[joderest]

ok, heres a guess.
Some older cars had a device on the carb/ throttle body that slightly increased revs on start up, then gradually decreased, my guess would be its shutting down too quickly. It could be vacuum activated or just a spring. Worth removing air filter and having a look, perhaps just needs a bit of oil to free it up, if its fitted.
Note>>>> 17 years is a long time for ignition parts, perhaps a mini service would help, plugs points cap and leads

 

[DREAMER NO2]

Orchid 87 Have you done all the items that are in the ht side , like distributor cap and the rotor, spark plugs and ht leads .I would do nothing till these have been replaced . Pull all the fuses out and clean them up and replace them ,,,do this one at a time and important -note from where you removed them from . Nect you can check the IACV valve remove it and clean it out with carb cleaner, or brake cleaner, i have even used white spirits , make sure there is no leaking hoses , and then refit --bit of a pain but it must to be done. .... Ho and you do have a small micro switch on the throttle quadrant , make sure its clicking and that its closed at stand still let us know how you get on .

 

[Orchid87]

Thanks both. It does feel as if something is just maybe a bit sticky so will try the above suggestions and see what happens.