Throttle position sensor

Fivewayradio · 03-23-2005, 11:49 AM

85 318i - M10. I've had this problem since I bought the car: Starts fine, when cold it idles about 1200, then as soon as it warms up and you'd assume the idle would come down it starts to rev up and down continuously between 700 and 1100 rpm. I've replaced and checked all the usual suspects (ISV, ICU, TPS). There ARE NO VACUUM LEAKS; I've replaced every vacuum hose, dipstick, valve cover gasket, everything.

Last night I adjusted the TPS so it doesn't click when you let off the gas fully. This fixes the problem. Of course it idles a little high so I adjusted the screw on the ISV and now it's all normal.

But as far as I can tell from everything I've read, this is a workaround and not a real solution to my problem, which I'm assuming is wiring. I assume that click when you let off the gas is the TPS telling the ICU that there's no gas and the ICV should take over.

Can anyone confirm this? Anyone got any thoughts on how to solve this problem?

Jared at Pelican Parts · 03-23-2005, 02:37 PM

It should click when you let off the gas..

Did you replace the intake manifold gaskets?

Fivewayradio · 03-24-2005, 07:16 AM

No, I didn't. But I don't think the idle stablizer valve is operating. I doesn't buzz or do any of the things people say it does, most of all, stabilize the idle. I've got two of them and they both snap open when I apply power to them, so I assume that means they work. I've also got two ICUs but I don't know how to test those.

golden · 03-25-2005, 04:02 AM

Faulty temp sensor?

hujev · 03-31-2005, 04:53 PM

Hi, I bought an 85 318i a few weeks ago to replace my now immobile saab 9000...

anyway, the problem is this: car runs, fires, idles normally after starting, but after it warms up a bit (say 5 mins) it then starts to have what i describe as a 'hiccup', rather severely, a misfire or fuel delivery problem...

symproms are the car intermitently either not firing one or more cylinders, or having a fuel delivery (mixture?) problem, and the result is jerky power (if idling will idle 'normally', with the 'hiccups' occurring appx. every 1-2 seconds, which causes the tach to appear to jump quickly to a higher idle for a split second, then back down. when running, the tach speed appears to go down...

even when this annoyance is happening, it's got decent power and so forth.

oh yeah, the last guy who worked on it (and gave up) left the throttle position sensor (?) cable assy disconnected... the one to the firewall under the intake manifold... when i re-attach it, the 'mpg' display on the dash pretty much stays up past '40mph' (ha!), even whilst idling, and the idle's all over the place!

i'm not set up too well to work on cars here in fairbanks AK, so haven't done any testing myself, but the previous owner had it in the shop off/on for the similar problem. the good thing is that the car's had a lot of basic service in the past coupla years... new idle valve, plugs and wires, cap and rotor, airflow (mass?) sensor, and also a head and oilpan gasket job, also valves. the various vacuum hoses were also replaced, and look good.

well, i'm taking it into the shop monday, but as i'm new to this town, don't know the mechanic, and of the last 2 places that did work before the car was mine, one closed, and the other gave up (gave up?? what the hell is that). so, i'm looking for ideas/advice to feed the mech if he gets confused or to help me if i've got to do trhe job myself!

one idea is possibly the distributor itself, though there might be more to this problem... maybe the coil?

fuel pressure, i believe, checked out ok in previous owner repair attempts... also, when flooring it i don't get a fuel starve, as i might expect in fuel delivery problem.

i did re-connect the throttle pos. sensor today to see the difference, and with this hooked up the idle hunts up and down (from about 1000 uo to ~14-1500 and back; and the vacuum ('mpg') does likewise (though not in synch with the idle rpm); from topped at 40mpg, down to zero, back up... in general, it seems to stay mostly at 40mpg when at idle (as opposed to at zero when throt. pos. sens. disconnected...); also the 'hiccup' seems a bit more acute...

so, i paid $1000 for this car, and despite this problem, i like the car and see the possibility to get quite a bit of life (and fun) out of it. i knew the problem when i bought it, and am convinced that if i can just get a competent mechanic, it's easily fixable...

scintaar · 04-06-2005, 07:25 AM

Fivewayradio.... have you tested the connector to the ICV/ISV? see if you get a voltage across the pins when the intake butterfly is closed.
The ICV/ISV basically bypasses the main intake and allows air into the engine when the throttle is off... I had a similar bit of trouble and a good cleaning of the ICV/ISV with some carb cleaner sorted it out immediately.

scintaar · 04-06-2005, 07:27 AM

Hujev... check the timing belt/chain was replaced correctly when the head gasket job was done. The problem definitely sound like the timing's been skewed.