2008 Suzuki 140 won't idle when warm

[Leelou77]

Motor help... 2008 Suzuki EF140, hard to start and won't idle when warm. Does fine for first cold start then issue after motoring then stopping. New thermostat, fuel pumps, coil, bulb and was serviced in April.
After motoring for a while, if you stop and put it in neutral it dies and if you try to start it, you have to hold the key on and throw it into drive to get moving again without it dying. Very tricky process. Runs fine with throttle just can't stop. Running out of ideas, any help appreciated!

[Moonlighter]

How is the primer bulb when the engine stalls after running? Is it sucked almost flat, or still firm?

[Leelou77]

It isn't flat or hard. Its pliable. Like you could pump it up a few squeezes.

[redlowrey]

ok run the engine on the muffs from cold start up, when the engine starts lift the warm up lever and run the engine at 1500rpm till it is hot, note if the engine is running smooth at that rpm, then slowly lower the engine rpm and note at what rpm the engine died, and whether it started getting rough before it dies or it just cut out.

Do you have a digital multimeter and know how to use it if so when the engine is hot with the key on check what the voltage of the temp sensor is, should be less than 1 volt. What it’s telling me when you hold the key in the start position the computer is commanding the iac valve to bypass air at 100 percent bypass.

Don't disconnect the temp sensor when you check the voltage. I think it is running too rich, when it’s hot if you lift the warm up lever and open the throttle a small amount it will start no problem it will be doing the same thing as holding the key in the start position, try it and come back on the forum with the results.

[Leelou77]

Engine runs smooth at 1400rpm. At 1500 rpm the motor begins to surge and shuts off. I have 2 volts at the temp sensor. And since the posting I have gotten a 3-1 code for the IAC valve. That was trying to warm it up. I got it warming up now. Its still surging but not as bad.
Update as I back down from 1500 rpm it starts to surge a little and just cuts out at 1000 rpm. I have 1 volt on the temp sensor when the engine is warm with the key on. I still have the 3-1 code.

[redlowrey]

I thought the engine might have been getting cold start fuel when the engine was hot but that’s not the case. Get your self a can of carbi cleaner or something that is flammable, run the engine to where it surges and spray around where the inlet manifold bolts to the head and into the throttle body and see if the rpm increases.

If there is no change in the rpm, pull a lead from each cylinder one at a time and see if you can pin point which cylinder makes no change when you pull the lead off.

[Leelou77]

Ok I will do that tomorrow. What are you leading to a possible dead cylinder? This motor had a different issue last summer that I chased and changed the IAC valve, new fuel pump, fuel lines, thermostat, bulb, impeller, fuel separator, filters, new oil 2x all to find out it was one of the coils. Ran fine until about a week ago then started doing this out of the blue.

[redlowrey]

If the engine runs ok with wide open throttle, there can’t be to much wrong one would think.

[Solarman]

Possibly fuel-rail pressure regulator weak, maybe at lower rpms? Just a thought?

[Leelou77]

Ok so with spraying the intake it steadies the motor and it quits surging.
pulling the plug wires the rpms drop on all 4 (done individually)

[redlowrey]

Ok if you sprayed the intake where the manifold bolts to the head and it stopped surging you just need to replace the intake manifold gasket easy job.

If you have an air leak on the intake runner it will usually effect the cylinder where the air leak is at idle or light throttle, but you won’t notice it under load or wide open throttle.

If it made no difference spraying the intake runner at the head but stopped the surging when spraying into the throttle opening that will mean the engine is running lean from a different problem.

[Leelou77]

Ok after rereading your post I realized we sprayed the wrong spot. We sprayed the IAC hose not on the intake manifold. Will re-do and post results.
Would an air leak in the intake cause the IAC to code?

[redlowrey]

Yes, what happens with an air leak the iac valve will be trying to control the rpm but it can’t. the air leak must be large.
If it had a small air leak from under the iac valve or throttle body or map sensor oring , the rpm would increase but the engine would run smooth.

For the engine to stall the air leak must be large it runs ok cold because it’s getting cold start fuel

If the engine runs fine on wide open throttle I don’t think you would have injector or low fuel pressure or map sensor problems.
You may have blown the gasket between the iac valve and manifold.