Over the last 3 weeks or so, I've had progressivly worse start-up. When cold (after sitting an hour or more), it acts like the engine is underwater...no fast idle at startup, engines slowly dies, and if I rev it, it feels like the accelerator cable is made of rubber, I get no real response, and it requires heavy throttle to get it to rev above 3000rpm. After a minute or two sitting warming up, and it starts to go away, I'll get intermitant power like it supposed to, almost like someone is playing with a switch that turns on and off one of the rotors. After 5 minutes, it's completly fine, full power, spinning tires, etc.

Until yesterday, when it never cleared up over a 50 miles highway drive. It would slid back and forth between power/choking several times a minute (10?), at low rpm (below 3500) it would stay in the choking mode, as RPM increased, the frequency and severity of the changes increases. These are sudden, lurching changes in power.



So, what could cause variable power loss?

Specs: thermowax disabled but not removed. Gutted cats, recent idle and TPS adjustment (about the same time this started, also when the thermowax was disabled). NA. small vacuum leak, and boost sensor is routed to empty nipple on the firewall side of the UIM (leak is where the broken old nipple is).

some ideas I had:

Fuel filter? Seems strange that it could clear/clog several times a minute like that

TPS? Possible...

Fuel pump?



This is obviously something that (1) clears up when engine warms up and (2) has degraded over time.

The first thing I thought when reading this was TPS. They will cause bucking/surging on off throttle. One thing you could try is routing your boost sensor line to the uim nipple right below the cold start assist injector thing (right above the lim). I don't know if it matters but that is where the line is supposed to be hooked up. Are you saying that nipple is broken off?

Yes, the normal vacuum nipple right where the UIM and LIM meet is broken off. I currently have a screw in there https://www.nopistons.com/forums/pub...#>/biggrin.png but it's still a small leak. I'm using a nipple that opened up when I disabled the thermowax.

I'll look at it this weekend, I was mainly hoping that no one would come on and tell me I've blown a seal...

What year is that car? How old are the spark plugs?



C

1988 S4. The plugs are probably 10K miles (but 98% highway miles). I've owned the car since April, and don't know the history, so things like the coils might be bad. If you lose a rotor (either seals, or plugs) what does it feel like?

you blow seals?



kevin.

Pazuzu, I have two spare upper intake mani's in the basement. If you want one, just PM me.. dirt cheap.

Thanks, but I'll probably just pull mine, drill out the old nipple, and either put a new one in, or block the hole off and use the spare nipple that I'm using now. It broke after I had reinstalled the UIM the last time, otherwise I would have drilled it out then and there (even I have limits to how lazy I can be when it concerns vehicle repairs https://www.nopistons.com/forums/pub... )

Anyways, I don't think this is a contributing part of my engine woes, since it did/does run properly at least some of the time. I'll see if the Seven in the local junkyard has the TPS still and maybe swap them. I'll have some time this weekend to dig into this a bit.

whats up Pazazu? i'll be wathing this thread to see what you come up with. i have the exact same problem but not a often. only happens when its extremly hot outside and the engines cold. the "accelorater cable made of rubber" is a good description. I can tell you this, i have the problem and dont have any vacuum leaks. my plugs are getting old. so you could probably rule out those two things.

forgot to say, i've pretty much ruled out the possibility of bad coils with mine(87n/a). and its not bad rotors or seals. no possible way the could cause the engine to surge back and forth like that if they were bad. i would be curious to see what an air/fuel gauge reads when this happens. engines either not getting enough fuel or air so i would look at that, or the unit that controls it. i'm not going to fix mine(to hell with it!), i'm putting a jay-tech intake and a four barrel on in a couple weeks. screw the fuel injection! good luck.