Hey guys, I've got an '85 that I've had for years and am always tinkering with. Most recently I've had an issue with the engine surging when I come to a stop at a light. It will die down and rev up over and over again anywhere between 400-1000 rpm's. Sometimes it will idle down enough on the 3rd-6th surge to actually cut off. And it doesn't always do it. Sometimes it will idle just fine.

I can hold the gas down just a little bit, and it will of course idle just a hair faster (around 700-800 rpm's) but it will be just fine and not surge at all then. I'm leaning towards the IAC valve or TPS but I'm not sure how to test either. Both were replaced about 8 years ago with new BWD units. And as far as electronic tools, my equipment list is only a snazzy little multimeter.

The engine itself is mostly still stock. The emissions stuff has been eliminated and the car has a hyper tech chip but those things have been there for years. I do have a decent little oil leak at the back of the intake that I've "fixed" twice now (and will be doing a 3rd time since I'm apparently not great with silicone) but I don't think that would be creating enough of a vacuum leak to be causing the surging though.

Thanks in advance for any thoughts or advice.

 

To test the TPS first determine which wires have +5Vdc, gnd and signal. Clip onto the signal & gnd and monitor volatage reading as you slowly & smoothly manually go from idle to WOT. If the value "jumps" or goes flat at any position, replace the TPS.

I'm not sure how to service the IAC save for a good cleaning and reset of base idle.

You might also check manifold vac for any signs of leaks.

How is fuel pressure both value and leakdown time?

 

65Z01 pretty much covered your question on the TPS and IAC...I'll answer about the problem your having with the intake manifold leak..First, you have to make sure your surfaces are spotlesslly clean, then instead of using RTV sealant, use "The Right Stuff" sealant made by Permatex. If you do your part, this is one sealant that wont come loose or leak..I used it on my China walls years ago, and have never had a leak since..It's not a silicon, it's a rubber product so it sticks like glue to the metel surfaces...Use this product one time, and you'll never use anything else again.....WW

http://www.permatex.com/products-2/p...t-maker-detail
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If your o2 sensor is very old replace it , my surging ended when I replaced mine.