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1999 Deville engine misfire no codes

1220 Views 7 Replies 2 Participants Last post by  rodbevan
I have had this problem from last year but the car has been off the road since November here in UK. At start up the engine runs fine for a short while, then begins to misfire, driving is ok, the car recovers but with lack of power for while, then runs fine. Idles uneven miss? Parking vehicle engine runs uneven, lack of power, and when restarted later runs uneven whilst manoeuvring, then lacks power for a while. The engine then settles down full power. I have to operate accelerator gently otherwise engine stumbles with lack of power. At idle engine is uneven, but rev engine and it has good power after a couple of splutters. I changed plugs last year to Bosch, these are fitted now. These are correct, checked with Rock Auto. I did try AC Delco plugs from Rock Auto, but these made the situation much worse with misfires and backfires on the road. I have no engine service lights and no current codes. Many thanks
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Have you checked codes? Even history codes can be relavent.
These only like AC plugs, it will not like others. Have you cleaned the TB? How old are plug wires?
I bet you have a simple issue like TB dirty, bad wire or coil going out.
If you have access to a handheld obd2 scanner with real time you can watch for misfires and it will show how many.
Another possibility is a vacuum leak, check the pcv hoses and grommets on vac hoses around the TB, the over pressure valve can stick or go bad causing vac leaks and bad running but it would be down the list.
Tb cleaning solves alot of idle and drivability issues. The flapper shouldn't rotate it pivots at top and ahould snap closed nice and quick. If still idling bad and can't find another leak time for scanner... My 98 had coil getting wonky and missed off and on for a couple weeks before went out.
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