Engine idle surges up and down when stopping at lights

[Larrysr1957]

I have a 97 ford 460 that has an idle surge and sometimes stalls when stoppingat traffic signals or signs. The mechanics has replaced the throttle positioning sensor and the idle air control and cleaned the fuel system. The idle rpm's still surges.there are no codes. Any help is appreciated

[jeromep]

Larrysr1957 wrote:
Thank you for the information and great advise. I will call around and ask if anyone has this test equipment.

I hope I didn't send you on a wild goose chase.

I might also add, you want to deal with a shop which does a fair amount of vehicle mechanical work on RVs and has the heavy lift capability to put 10 tons of weight into the air. If the shops you are dealing with don't have this, I'd be locating a different one. In reality, when you take an RV to a mechanic, they need to have the skills and background to deal with large, heavy vehicles. Think of it like this, your Class A and C are less like a regular vehicle and more like a UPS truck; they need to be worked on by a shop that knows that kind of stuff.

[Larrysr1957]

Thank you for the information and great advise. I will call around and ask if anyone has this test equipment.

[jeromep]

Larrysr1957 wrote:
I have a 97 ford 460 that has an idle surge and sometimes stalls when stoppingat traffic signals or signs. The mechanics has replaced the throttle positioning sensor and the idle air control and cleaned the fuel system. The idle rpm's still surges.there are no codes. Any help is appreciated

I think you need to find a different mechanic. They are just throwing replacement parts at the problem, they don't really know what is happening. If they knew what was happening they would have already fixed it. I really don't like it when mechanics throw parts at a problem and you pay for their experiment.

I don't know what the issue is either, but my advice costs you nothing and if I were in your position I'd be more than just a little annoyed at paying for something to not be fixed. But I do know this, 97 was the last year of the 460 on a vehicle chassis. For MY 1998, the V-10 was introduced and a totally new era of computer control was introduced.

The 460 was never built in an OBD or OBDII equipped vehicle, therefore getting codes out of it for diagnostics requires much older hardware. They are technically Ford EECIV (Electronic Engine Control 4), vehicles. Ford used EECIV in just about everything from like 1982 all the way till the OBD era. EECIV had numerous changes and variations over all those years and the computer unit was basically entirely different from vehicle to vehicle. My guess is that only a Ford dealer, or a very well equipped independent shop, will have the proper equipment, probably sitting in a corner or on a shelf, to get the codes and information that might lead to a direct fix. If you can find a dealer or mechanic with a Ford SBDS (Service Bay Diagnostic System) with the 168-pin connector, which is probably what your 460 has to connect to the onboard systems, they might be able to find out what is occurring, assuming that the on board sensors are able to identify an issue.

My point is that if you have a mechanic that is throwing parts at the problem, they don't have the right equipment to complete a diagnostic.

[2112]

Do come back and let us know what solved this problem.

[Jarlaxle]

wa8yxm wrote:
97 Fuel injected or carburetor.. That "Hunting" is a sign of running rich as i recall on a carbureted engine. Might be dirty injectors. but sure sounds like a fuel issue.... Alas. Not a ford man...

Ford went to EFI by 1989.

[doxiemom11]

I had a GMC Jimmy that did that. EGR valve kept clogging with carbon. Hubby would take it off, blow it out with air compressor and then it was good for about 3 months. If we didn't do that, the idle got worse and it would stall, service engine light would then come on. The surge is what told me it was starting again and he needed to do that.

[wa8yxm]

97 Fuel injected or carburetor.. That "Hunting" is a sign of running rich as i recall on a carbureted engine. Might be dirty injectors. but sure sounds like a fuel issue.... Alas. Not a ford man...

[Yankee_Clipper]

Two items that may be a reach: a) check to ensure your gas filler cap is sealing. b) my old 97 460 was hard on exhaust manifold, and warped two of them on the passenger side; both time the engine ran rough until the replacements went on.
Those exhaust manifolds also spit out can bolts as the warp got worse, and could crack a head. Hope this helps,

[Jarlaxle]

Pretty sure those engines are speed-density, no MAF sensor.

Agrees with the previous posters-sounds like a vacuum leak.

[Lt46]

You don't have a MAF sensor, rather, a MAP sensor. When my 97/460 did the stall at lights I first cleaned and then ultimately replace the IAC which solved my problem.

[Larrysr1957]

I will check the mass air flow sensor
Thank you

[rjstractor]

A dirty or faulty mass air flow sensor will cause this issue IIRC and not always throw a code.

[2112]

My 1988 Explorer did this and the cause was a cracked intake manifold. It was sucking unmetered air.

[naturist]

With gas engines, surging is sometimes due to a vacuum leak.