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1988 vw cabriolet

Every time I go to start it ,it runs ruff for about 30 seconds it sometimes
Will even stall but Then it will be fine . But will stumble once I com to a stop and take off again …It had new spark plug wires done before I bought it and I just did the fuel filter. I run a few cans of injector cleaner But no change . It also stumbles going up hills when the fuel is 1/4 or lower .any ideas?

Could this be a vacuum problem?

The stumbling could be many things. It could be a vacuum leak, it could be related to the IAC valve, among other things. Pumps that are located in the tank (which I take is where yours is) are cooled by the gas they are immersed in so maybe it is having heat issues when it loses its cooling. Like I said: many things could be wrong.
Have you checked the fuel pressure?

car haas two fuel pumps a slave in the tank and a main under the car. vw of this time had problems with electrical connections check the contacts at the coil. and the grounds

Will have to agree with Remoco and Hot Rod on this one… They hit it right on the head

This issue is a common one on that vehicle…it is the air idle control valve…its a silver canister located near the intake of the engine…inside is a circular disc with holes in it…this disc rotates…(or tries to rotate) to allow a “controlled vacuume leak”…this controlled vac leak will raise and lower your idle…if AND WHEN that control valve gets gummy or clogged with soot or carbon it cannot rotate and provide your engine with the correct amount of vacuum leak to control your idle… Its textbook VW

I usually soak mine in diesel fuel overnight and then use compressed air and carb cleaner to try and free up that disc…works most of the time

Blackbird

yes i think you guys hit the nail on the head