IS INTAKE MANIFOLD CAN AFFECT TIMING?

  • Tiny
  • pokalay
  • 1989 Toyota Corolla
  • 100,000 miles

Idling is to rough. I tried to adjust timing but the timing is to far from 10deg almost 20deg I think. I tried to adjust idle mixture screw but it wont help. I changed sparkplug, cleaned the carburetor and distributor's contacts but the idling still moving up and down. Already checked vacuum cables.

Tuesday, September 13th, 2011 AT 10:01 AM

6 Answers

  • Tiny
  • mhpautos
  • Expert
  • 29,842 posts

These do have a habit of sucking in the inlet manifold, spray a little starter fluid around the manifold, if the revs pick up there is a leak, check this first.

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Tuesday, September 13th, 2011 AT 11:46 AM
  • Tiny
  • KHLow2008
  • Expert
  • 41,938 posts

Improper valve adjustment is another possible cause. So would a bad PCV valve and unequal engine compression pressure.

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Tuesday, September 13th, 2011 AT 12:11 PM
  • Tiny
  • pokalay
  • Member

My engine is 5af shim type and no need to adjust valve clearance. I tried to replaced gasket on intake manifold hope this will end up my trouble. Thanks for the quick reply.

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Thursday, September 15th, 2011 AT 5:34 AM
  • Tiny
  • KHLow2008
  • Expert
  • 41,938 posts

Shim type does not mean valve adjustment is not necessary.

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Thursday, September 15th, 2011 AT 12:48 PM
  • Tiny
  • mmprince4000
  • Expert
  • 8,715 posts

Shims are adjustable, they do wear. Clearence should be.010 on intake and.008 on exhaust (cold engine). You simply put a new shim in.

But the intake gasket can leak and if large enough will cause significant loss of power.

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Thursday, September 15th, 2011 AT 1:26 PM
  • Tiny
  • pokalay
  • Member

Idling is now good and the engine is fine but I cant set the timing
to 10deg. I plugged 2 vacuum from distributor advance diaphram. 15deg is the lowest degree I can set. I already changed and checked the timing belt and set all timing marks, set the pulley at 0" TDC at the compression stroke and rotor at the spark#1. My current timing is 15degree. How can I reach 10 degree? Is my distributor faulty or my engine need to be top overhauled? My engine is toyota 89 model 4af carb with egr system.

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Wednesday, October 5th, 2011 AT 8:42 AM

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