henreezy

I’ve been having an idling issue with my 85.5 944 and am desperately searching for a solution. The car had been starting strange and making sharp crank sounds before starting after a couple gos, and then surging between 1-3k RPM. Sometimes it’d start fine, sometimes it’d start fine and then develop the same surge while driving. In my latest attempt to fix it, I replaced the ICV and icv hoses, cleaned grounds, and replaced the manifold gaskets. Also did the heater control valve while in there. The PO had the vacuum lines replaced (Lindsey kit). The car after that still started bad at first then would start and die quickly, and then for a few good tries started great and idled perfect 1-1.2k RPM. Few minutes later wouldn’t start or faded.

I plan on replacing the throttle bottle seals and potentially looking into the TPS but need to do more research. If anyone can help me solve this I’d be forever greatful 🙇‍♂️.

best,
Mark Bogle

Jfrahm

Why not follow up in your other thread?

henreezy

oh sorry, new here and not sure on the thread etiquette. I believe I did a better job describing my issue in this one.

peanut

you're not going to get a better response by starting a new thread on the same issue ................what will happen is
1, it will get confusing trying to follow 2x separate threads and
2. members that responded to your previous thread with help or advice and did not receive either a reply, or thank you, might not feel inclined to continue .

henreezy

Right, I now realize that. I apologize for wasting space in the thread forum. Back to the Haynes manual!

bonus12

It sounds like a vacuum leak somewhere.

From Clarks-Garage.com, a top notch resource:
A faulty throttle position switch (TPS) can result in a number of poor running problems. Because they can result in such a large number of problems, faulty switches often go undiagnosed. The other thing that makes TPS problems difficult to diagnose is that they quite often only appear when the engine is warmed up (throttle position switch warmed up).

The following lists some of the symptoms that MAY indicate a problem with the throttle position switch:

• Poor idle - particularly a high idle condition
• Engine cuts out to an idle condition during acceleration
• Poor power at various RPMs (various throttle positions)
• Surging idle
• Misfire
• Stumble during acceleration
• Intermittent boost problems (turbocharged cars)

Chalt

No need to leave the forum. Copy what you thought was written better and paste it in the first thread. No one's wanting you to leave. We'd like to help.

henreezy

I didn’t intend it to come off that way, just hittin the books. This forum has helped me more than anything so far

henreezy

ok, those are all symptoms I have. Going to do the tps, throttle body orings, although I can’t find the two side replacements, and some fuel line/ vacuum testing. Thanks for the info and I’ll report back soon 🫡

Jfrahm

From the other thread: J boot cracks, ISV elbow damage, etc.

peanut

Mark when troubleshooting a problem its always best to follow a recognisable sequence of checking and testing. This approach prevents random component replacement or setting adjustments which are not only expensive and unnecessary it also prevents making the situation worse by adding additional issues.

First of all, from what I understand from your description this would appear to be an intermittent issue,... or at least from what you describe it is not a constant issue with consistent symptoms.
This makes it unlikely IMO to be due to a vacuum leak as I would expect the engine to display the same symptoms and performance every time you started or drove the car.

The second observation that i would make is that it is unlikely to be due to the TPS which is simply an on/off switch, The TPS tells the ECU when the the throttle is completely closed when idling or decelerating.
Provided that the TPS is set correctly and functioning (multimeter test ) I think its safe to disregard it as the issue.

It would be extremely helpful if you could post a video of starting and running the engine at idle,.... then blipping the throttle momentarily a few times to rev the engine off of idle to show throttle response and pick up off of idle

henreezy

Hey all, I have some updates. So after replacing the tps, spraying some contact cleaner, and a throttle body main o-ring replacement, the car started up right away with a consistent idle. A couple of starts still cranked hard, and a couple had a continual revving issue. More often than not it’s idled 800-1100rpm than it has surged. Still not perfect and is bogging in low gear.

To be more specific on the starting issue, when starting, it occasionally starts, sits 200-600 RPM, dies or dies when pushing throttle. Or starts, sits 1200-1600, begins climbing. Other than that it’s right in the middle and perfect.

I also attempted an O2 sensor replacement. Bad move. Used my blue wrench and everything. If anyone has stuck sensor solutions before I take it to a muffler shop LMK!

Thank you guys for any and all of your time and I appreciate all responses!

Zirconocene

If you suspect a vacuum leak, how about a smoke test? That will give you a pretty direct indication of where things might be going wrong.

The other easy test you can do is to unplug the vacuum lines from your fuel pressure regulator and damper, and see if there's any fuel in those lines.

Separately, how's your air filter? That's another easy check.

Cheers

peanut

.

you are still continuing to replace parts randomly in the hope that suddenly this engine issue will be cured. Those original parts may be perfectly good parts and the new parts you fit could very easily be faulty...(as a lot of new parts often are.)

You need to start following a proper sequential sequence of checks and tests so that you can eliminate components that are sound and narrow down on possible problem components otherwise you are just shooting in the dark and damaging sound components like the 02 sensor !

I have already explained that this issue has nothing whatsoever to do with the TPS and explained why that is so, yet you ignore that and go and mess with it anyway...but not apparently test its correct function with a multimeter ?

I can understand your frustration but this issue is only likely to be resolved by testing things properly and posting the results so that people on the far side of the World can have half a chance of assisting you .

Chalt

Aside from the O2 sensor...
Can you be more specific:
1) You say it started right up with a consistent idle after working on throttle body.
2) You say a couple of starts cranked hard. What do you mean? Wouldn't start? Started after cranking a long time?
3) You say a couple had a continual revving issue. What does that mean?
4) You say idles 800-1100 rpm. This isn't bad. But then you say bogging in low gear. Is it driveable? Are you driving it?
5) You say sometimes 200-600 rpm, 1200-1600 rpm, Other times between that. So is everytime you start it a different idle rpm? Is the problem consistently poor idle, or is it intermittent?

Can you drive the car?
Does it start every time?
Does the idle settle down?

Have you visited Clarks Garage? It has troubleshooting for idle issues here: Troubleshooting Engine, TS-01