It started last year. My idle speed became erratic. It would drop down low.I thought it was the carb. So today I changed it, but the idles speed is still erratic. There is no manifold leak. What I did notice, was when I turned my lights on and off, it would affect my idle speed! Holy ****, WTF is that? I'm gonna replace my ignition switch and see if that might be the problem. Any other ideas?

 

I fixed a friend's 89 ultra a few years ago that was doing almost the same thing. when he turned the spotlamps on, the engine would miss. I went over all the wiring in the fairing, and the grounds. Apparently both inner and outer fairings were replaced at one time, and the wiring was a rats nest. The ignition and lights were on the same circuit, which made the voltage drop with the lights on. All I can say is follow the wiring diagram, hand over hand each connection, clean or replace as necessary.

 

check the VOES switch rubber hose for cracks If it still exists

 

I agree, likely could be voes hoses, or any pollution control or fuel tank venting hoseblocked or cracked. Also ignition module, maybe sparkplugs, coil. Are you sure there is no manifold leak? Spray wd40 around manifold area, if idle speed increase, there is still a leak somewhere.

 

Well I looked at the bike today with a fresh mind. Pulled off the instrument panel, all the electrical connections were tight. So I looked at the ignition module next. I noticed the ground wire had worked its way between the mounting plate and frame, and was squshed flat. When I pulled it out, I mean it was FLAT. Hmmmmm....could the wire be frayed or broken? So I cut it short and crimped on an extension. Then I covered it with a protective wire cover and reground the wire. fired up the bike, it ran kinda crappy at first, but it's only in the 30's here in Chicago. Once warmed up, I took it for about a 30 minute ride. It never missed a beat. I played with the lights, on and off. The idle speed never fluctuated. Hopefully that was the problem. I'm keeping my fingers crossed.

 

Congrats! hope that completely solved your problem...flaky grounds can cause all kind of weird things to happen.

 

Hello,[/align][/align]The short story...sounds like either the electronic module is going out (not likely, they work or they don't) and/or the sensor plate is going out (heat damages sensor plates over the years). If both are somewhat old and have seen better days my money is on the sensor plate.I went through avery similar issueon my 1885 FTLC (which has thesame electrical components as your '88 FLHS). Nice bike by the way...I removed the fairing and placed a HS front end on mine...there ya go. Anyway, an easy way to tell if the sensor plate is bad using a hair dryer...no ****! HD service tech told me...I tried it and found my problem (sensor plate) ok too the test...remove nose cone cover and gaskets, START THE BIKE, keeping an idle...start heating sensor plate with the dryer. If the bike starts to cutout, etc. and dies...replace the sensor plate. If the bikes doesn't cutout your module could be bad or you have a bad wire somewhere in the electronical circuit from the ignition switch back to the main breaker.lf you have time take the serivce manual and follow their test procedures...kinda cool.[/align]Buy the way...that ignition switch isobsolete...can't be had easily. Seen one on ebay for $250 which isn't to bad considering. I'd put money on the sensor plate and module and not the ignition switch. And lastly, if your electrical module is original and you want to replace it, tyou will need to buy the electrical harness to connect from the module to the new sensor plate (more money). Good Luck and happy motoring![/align]