rough idle – replaced tps, solved it temporarily??

eric.t · Post by **eric.t** » 21 Jul 2017, 05:25

Hello all,

94 850 turbo

Pretty new to maintenance on this thing – reading all I can but I’m a little stumped. Appreciate whatever input anyone has.

Had an intermittent issue for a while with rough idle, especially after driving the car hard. ex. If I floored it going up a long freeway onramp then as soon as I got back to surface streets it would shudder around at stoplights and very low speeds. Strangely the problem would usually resolve itself in a few days if I drove it gently.

I don’t quite remember what the code was, or what I turned up while researching, but I ended up getting a replacement throttle position sensor. Finally got around to installing it, and cleaned the throttle body while I was there. Its been driving much more smoothly since I did the work a few days ago, and the code it was throwing hasn’t returned. I even pushed it pretty hard up hills, on freeway etc. just to test its usual problems and it seemed solid.

I was working on an unrelated problem tonight (ecc) and took it for a test drive, where I maybe got a little too aggressive…original shuddering has returned, plus it sounds like its having a hard time starting now.

Questions:
• Am I even on the right track? Something else I should be looking into for this behavior? Idle control? leaky hose somewhere?
Not getting any relevant codes.

• tps adjustment – Do all TPS units “click”? Bought a new (old stock) bosch unit, same as what’s in there, but while adjusting it I couldn’t hear anything even with it right up to my ear. For that matter I’m not hearing a click on the one I pulled out either, but that probably doesn’t mean much. Should I think about ordering another one or are some just really really quiet?

Thanks!

Post by **erikv11** » 21 Jul 2017, 07:41

TPS should be smooth throughout the range, no clicks at all.

I am wondering if there is a small vacuum leak somewhere in the intake or the boost path (induction hoses). Those can be a pain to find.

Post by **Clemens** » 21 Jul 2017, 15:48

how old is the ignition system?
I guess yours has an automatic tranny?
I am asking because i had the same problem after buying mine, which sat in a dealer's lot for a while. After doing a few ATF drains and refills it got better, new wires, plugs and rotor/dizzy fixed the problem completely.
Why, I don't know.

eric.t · Post by **eric.t** » 21 Jul 2017, 19:02

Good to know that the tps doesn't click in this car, maybe I was in the wrong forum when I kept reading about that. If that's the case though, is there something special I need to do to calibrate it? or is it just relative and the computer can figure it out?

Automatic trans,
Funny you should mention ignition stuff. Just did all the secondary ignition stuff a few months ago and that helped a lot (rotor, cap, plugs, wires, coil - all new OEM, bougicord wires), always seems to end up back with this problem though. Replaced an upper engine mount bushing also, that helped with the shaking.
Car had been neglected/sitting for a long time, slowly chipping away at it...Seems like theres a lot of stuff in this car thats in an "almost failing" condition, so feels like my problems often involve more than one system or part.

Thanks for the suggestions about vacuum leak and atf I'll read up on that and poke at it some more.

Thanks for the help

Post by **Clemens** » 22 Jul 2017, 15:00

Hard starting: does it smell like gas (flooded, too rich) or is it a no fuel situation? These days clogged fuel filters are rarely the problem anymore, but the fuel oh p relay and the fuel pump are known offenders.

Post by **Clemens** » 22 Jul 2017, 15:23

Hard starting: does it smell like gas (flooded, too rich) or is it a no fuel situation? These days clogged fuel filters are rarely the problem anymore, but the fuel
Pump relay and the fuel pump are known offenders.
Erratic fuel pressure could be the cause, i believe.

eric.t · Post by **eric.t** » 07 Aug 2017, 19:19

No gas smell, but thanks for the input.

Mostly solved!
In case anyone else with the same problem finds this –
I took apart and cleaned the IACV, it was pretty gross in there.
Also looked around and did find an old/loose-ish vac hose going to IM. Tightened that up with a new clamp at the same time.
Seems to have fixed the problem! For now anyway...
Thanks for the suggestion to check vacuum stuff.

Next up is tackling a clogged PCV...

Post by **scot850** » 07 Aug 2017, 23:50

Glad you got one issue hopefully resolved!

Neil.