Caterham Roadsport Cold Idle Fix MAP

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The Caterham doesn't like idling when cold for about 30-60 seconds it needs constant throttle blipping to not stall out.

After reading some general 'what causes a car not to cold idle' type pages, I had a check of the MAP sensor (Manifold Absolute Pressure) and vacuum hose from the manifold.

Turns out the 4 year old hose is already perished/split! - the worse end is on the manifold (literally fell off as I moved it) and the MAP end was splitting too.


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Manifold end

Manifold end (left) , MAP unit end (right)

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I chopped these ends off and managed to get the hose back on the manifold after a great deal of effort

  • tip 1 push up the washer bottle so it comes off and drops down
  • tip 2 put the vacuum tube end for the manifold on just the tip of the MAP unit, this widens/stretches it just enough to then get it on the manifold. (Boiling water didn't seem to soften it which is usually what I'd do for tubes)
  • tip 3 use pliers (from underneath) on the tube once its partly on the manifold to push it home, I never managed to get mine fully home though.

Anyway the upshot was I started it in the garage and let it go without touching the throttle, it kept going and didn't stall :), although I almost gassed myself.

MAP unit test

Oh and it is easy to test the MAP unit too with the tube off (at least get an idea its working right anyway)

  • Paperclip down the middle pin, connect to +'ive on voltmeter
  • Negative to earth somewhere nearby.
  • Ignition on, not start, should be about 5v (mine was 4.7v) on the meter.
  • Find a rubber tube and stick one end over the MAP unit, suck on other end and watch the voltmeter, it should drop more the harder you suck. With a reasonable amount of sucking it should drop to ~3v and it is a linear 'sucking to voltage'.


I happened upon a thread here that sounds like they are talking about this vacuum pipe splitting so could well be a common fault for newer Sigma Caterhams?


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