I have a Merc 496 HO that makes an Exhaust Manifold Popping noise only at Idle, it also surges at Idle. I replaced the plugs, fuel filters, new gas, made sure the fuel pressure regulator vacuum hose was not cracked. Any other ideas? Thanks.

Dave

You very well could have an IAC going bad. Has it ever been replaced?

What is an IAC? Forgive my ignorance.

Idle Air Control valve.

best to have a real Merc tech work on your engine and if you have DTS there is no IAC. --- half of 496's out on the market place are DTS apps so half do not even have IAC's. Does your have mechanical throttle and shift or DTS

Your location ?

MY GUESS POSSIBLE exhaust manifold gasket leak.per your script..

next areas ---- to look at for your problems

fuel pressure ?? what is it ?? you never mentioned that. --- lean popping ??? What cool fuel set up do you have ???

compression testing numbers ??? is it popping 4 sure thru the exhaust ????

ignition and spark check along with scan to see if any faults ????? --- spark plugs good and or arcing of something including the same with the spark plug wires. Make sure they are all connected real well. The port side very rear wire boot has a tendency to come loose and or can be very hard at times to make it connect 100 percent.

Thanks for the input. I do have a mechanical throttle and shift, no DTS. I have the Gen III Cool Fuel Module, new filters. I located the IAC. The popping happens every 10-15 seconds. No leaks around the exhaust manifolds. I have some more investigating to do. Sea Foam through the throttle body was mentioned to me as a way to clean things out. As soon as I add power, it all go's away. Only at idle.

Mechanic in the bottle is not your problem fixer. Actually real shops whom work on these for a living - like people whom use a ton and over base the fuel with snake oils because it helps peels off the paint inside the gen 3 cool fuel assembly causing all kinds of problems especially with the injectors.

you need to run a scan of the engine and watch the parameters along with the PWM of the IAC.

Fuel pressure testing another good idea as well.