Erratic engine ??

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sideshowbob
Posts: 247
Joined: Mon Aug 01, 2011 2:18 pm
Location: Hampshire UK

Erratic engine ??

Post by sideshowbob »

Car is an '89 635 CSi, and recently has been a poor starter and suffered a bit of misfiring when under load.

Has been into local garage and had distributor, rotor and all spark plugs and ignition leads renewed. Also done a smoke test and no vacuum leaks

This has cured the poor starting and misfire but it now has developed some new problems which the garage think are related to the AFM.

The 'new' problem manifests itself in several ways at tick over the engine will suddenly rev to say 1500rpm and then fall back to normal and then repeat this several times before settling to normal or stalling, this happens from cold.

Then when driving at say 2000rpm the revs will suddenly drop to 1500rpm and immediately kick back to 2000rpm ...with a jerk. Additionally the mpg indicator violently swings from 24 ish mpg to 50+mpg then immediately returns to 24ish.

Finally the above scenario can happen several times in succession resulting in a feeling of loss of revs and power...this seems to happen more prevalently when the engine is hot.

Can any one suggest what is wrong is it a fault with the AFM or could it be related more to a sensor that links into the AFM.

Any help would be appreciated
sideshowbob
Posts: 247
Joined: Mon Aug 01, 2011 2:18 pm
Location: Hampshire UK

Re: Erratic engine ??

Post by sideshowbob »

Have been told that this is symptomatic of a failing crankshaft sensor....anyone on here had a similar problem and fixed it with a new sensor......anyone ??
sideshowbob
Posts: 247
Joined: Mon Aug 01, 2011 2:18 pm
Location: Hampshire UK

Re: Erratic engine ??

Post by sideshowbob »

Just a quick follow up...managed to solve problem with help from Rich at Fritz Bits.

After quite a bit of investigation it turned out to be a failing throttle position sensor. Replaced and now engine runs perfectly.
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635sharknose
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Joined: Fri Sep 13, 2019 4:58 pm
Location: The Netherlands
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Re: Erratic engine ??

Post by 635sharknose »

Thank you for sharing this information.
I'm glad you have solved the issue!
Paul
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Instagram: @635sharknose
1987 635CSi Bronzitbeige
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