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Author Topic: An interesting cure!  (Read 1160 times)
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Angle Grinder
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« on: 20 February, 2013, 03:16:08 PM »

This isn't likely to assist many Thema drivers as it happened to my Series 2 V6 Auto and there's only 2 of them in the country (counting mine), but I'd be interested to hear your theories on why it occurred.

About 2 1/2 yrs ago I noticed that my V6 was developing a slight idle hiccup. When the car was idling or crawling at parking speeds, she would suddenly surge from low revs up to 1600rpm and this usually happened after a dip in the idle speed. It was as if an ECU was suddenly thinking the car was about to stall and it then decided to give it a gun.

I changed the engine temp sensor as the surge always seemed to happen at the same temp point. I also changed the plugs, fuel filter, air filter... but none of this really made much difference.

I then left the car unused for ~3 weeks over winter. She is normally used every day and lives outside (Themas are tough, much tougher than most cars of their period). After this long damp hibernation, she would not start. The problem was traced to a weak spark at the plugs so I changed the dizzy cap, rotor arm and plugs... VRRRROOOOOMM! She fired up instantly and idled absolutely on the button by the textbook setting of 780 - 820 rpm.

The idle surge is completely gone. So the surge appears to have been related to a worn dizzy giving a weak spark... any thoughts on why this would cause idle surge?
« Last Edit: 20 February, 2013, 03:40:02 PM by Angle Grinder » Logged

Current Cars: 1994 2.0 VIS Thema Station Wagon, 1967 Flavia 1.8 PF Coupe.

Previous cars:
1983 Prisma 1600
1991 Thema 16v i.e. SE
1988 Thema 8v Turbo
1992 Thema 16v i.e.
1983 Gamma Coupe (manual)
1993 Thema VIS
1994 Thema VIS LE
1990 Thema 2.8
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