Idle drops and comes back when first started

Tiny
AMENDELSON
  • MEMBER
  • 1988 TOYOTA PICKUP
  • 3.0L
  • V6
  • 4WD
  • MANUAL
  • 304,000 MILES
Engine has head gasket leak on cylinder six. Plug no longer fires and last time I pulled it the head threads came out with it. That said, when the engine is cold the idle drops and comes back, drops and comes back. When hot it holds an idle just fine. Truck still has lots of power even with a bad cylinder. I need to change the head but before that, any suggestions on the idle problem?
Sunday, August 13th, 2017 AT 7:14 AM

2 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
Hello,

The engine will never run right with a bad cylinder and a blown head gasket. Replace the gasket and the engine should run okay once again.

Best, Ken
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Monday, August 14th, 2017 AT 7:18 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,240 POSTS
The varied idle can be due to the bad gasket. It would likely leaking between cylinders and the engine then stops firing on two cylinders until it heats up and the head expands and the leak slows enough that the other cylinder comes back. It essentially loses the power from those two cylinders, slows down and then speeds up as the rest fire.

I would get it changed now, as the leak could easily cause it to hydro-lock and bend a rod/snap the crankshaft. Plus the unburnt fuel is probably washing the cylinder and you may end up replacing the engine, not just the head gasket.
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Monday, August 14th, 2017 AT 9:53 PM

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