3.0 idle surge

[2wheelmadman]

I'm just about ready to pull the plug and wave bye bye to this piece of junk!

It's a 1999 3.0 L GM, I've had the valves done, re-set them, checked compression, replaced the riser, the intake/exhaust manifold, t-stat, wires, plugs, distributor, coil, rebuilt the carb, replaced all hoses, checked timing, fuel filter, oil and filter, and every other thing known to mankind, and I just cannot get this engine to idle!

if I set it for below 1100 rpm it drops further and then surges back up to 1200 rpm and will keep doing that indefinitely.

I can't run it like this, as the shift into gear at 1100 will take the drive out sooner or later.

Has anyone got any ideas or suggestions?

Thanks guys.

 

[victorc1]

Re: 3.0 idle surge

Sounds to me like you have a problem with the idle speed control sensor if its fuel injection or the injectors are clogged, if its carburator check your choke or the carb is pulling in air from somewhere.
If you're planning to sink the boat I'll buy some parts from the motor.

 

[Don S]

Re: 3.0 idle surge

Let's start from the beginning.
1. Are we talking Volvo or Mercruiser here.
2. What is the full model number and SN of the engine.
3. You have changed a lot of parts, have you done any testing of any kind.
Compression tests, leakdown tests, vacuum tests, timing set (while in base timing) etc.
4. You have been replacing a lot of parts without curing the problem. How much of the new parts have been adjusted to spec following the service manual for whatever you have. PS Clymers or Seloc doesn't count as a manual

 

[fossill]

Re: 3.0 idle surge

Sorry, but unless your very mechanically inclined and have a thorough understanding of engines, especially diagnostic techniques, most people shouldn't be working on them. You can spend a fortune throwing parts at the issue and still not have it right or take the money and have a tech look at it.

 

[2wheelmadman]

Re: 3.0 idle surge

Guys,

I build drag bikes for a living, I have a pretty good understanding of engines in general,but apparently however not marine engines.

I didn't throw parts at this, each part replaced was prefaced by condition or necessity and/or testing.

This is a two barrel normally aspirated setup, not real complicated but obviously I'm missing some technique or lack the knowledge to find the issue. Is there something about a marine engine that I could have missed?

 

[Don S]

Re: 3.0 idle surge

I did ask four questions, could you answer them?

 

[Zeeter]

Re: 3.0 idle surge

Thats a basic engine. A surge usually means an air leak or a vacuum leak, same thing. The engine can be getting air from somewhere other than through the carb. Also dont forget the vacuum advance solenoid on the distributor. Those diaphragms can crack and that can cause a timing surge up and down.
Are we sure all the vacuum lines are plugged in where they are supposed to be and there are no cracks or leaks in any of them?
Spraying some WD40 around may help you find a vacuum leak.
The only onther thing I can think of is a throttle kicker or choke fast idle that can't find where it wants to be.
A vacuum guage would tell you alot.