peanut

Mark 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.

This would ,...more that any explanation.... help us to help you.

From your description this would appear to be an intermittent fault and quite to be likely due to either a component breaking down or a breakdown of an electrical connection somewhere.

An idle that rises and stays high is generally due to a lean mixture, either too much air, or too little fuel, or a combination of both..

The fuel and air delivery to the engine at idle is governed by the ECU in response to crank speed, air flow and engine temperature.
With an 'erratic Idle' issue we should be looking at and testing the components and associated wiring that the ECU uses to determine fuel and air delivery and ignition .

If initially we assume that the ECU is working correctly I would be looking at the fuel delivery system and air flow .

I would suggest that you buy a simple cheap pressure meter and attach it to your fuel rail permanently until this issue is resolved.
The meter will show if you have a consistent and correct the fuel rail pressure . it will also provide you with a 'leak down' test . If the fuel system is losing pressure after switch off that might explain the hard starting symptoms.
In addition to this it will show if there is any variation in fuel pressure when the engine idle speed rises or becomes erratic from moment to moment in real time

This would be a good first step at this point and might allow you to eliminate quite a few possible fault sources

henreezi

Thanks Peanut for this detailed reply. I'm sorry for the late response, I've had a bit of a hectic schedule. I will try to get the issues I'm having on video when I'm home working on it today and this weekend. As a brief summary on what's been done total and since my last post (just throwing parts at it until now):
-New ICV/ intake manifold gaskets
-Lindsey Racing vacuum kit
-New distributor/fuel lines
-o2 sensor replaced/exhaust manifold gaskets
-TPS replaced

I. I am going to rent a fuel pressure tester from AutoZone this weekend as well as testing for vacuum leaks with starter fluid.
II. Every upgrade makes a subtle difference. For instance, the surging issue I had on top of the high idle is eliminated completely now (I suspect the tps/icv did the trick)
III. If anybody can help me locate where to buy the two smaller throttle body O-rings (I have the main one) I would appreciate it so much. Or knows what dimensions they are?
IV. As of now i plan to do those tests, replace the throttle body O-rings and recalibrate it.

I know a lot of this may be meaningless without the video, but I'll get that on the forum ASAP!
I feel indebted for all the help this forum has provided and appreciate all the accrued knowledge you guys have to impart.
For those who care, I just bought this car as my first after driving my dad's ranger till now. I'm 20 and in college and working on as much of a budget as you can with a 40 y.o. 944. I loved these cars the moment i saw one and would love to get mine in working order. I have a great "mechanical" support system (minus a lift) as my dad and brother are car guys. It's a story I've seen many times on here XD, just hope mines a success one!
Thanks Again and will update soon!

henreezi

Thank You Chalt!
I have visited Clark's Garage as im becoming a regular there. Those are all great questions and ill try to respond to them as detailed as i can.
5.) The car will start 2/3 times with the outlier being a no start/multiple crank/engine shimmy combo.
-Three Follow Ups-
A. Can You Drive the Car?
Yes, i can,and its a blast when right!
B. Does it Start Every Time?
No, struggles when cold, although similar when hot. Never takes more than three attempts to start. Once started then its either idling too high 1100-1600 or extremely low 200-600. Like a slot machine, every once in a while, it hits, and it sounds impeccable with its aftermarket exhaust comfortably idling around 800-900 RPM.
C. Does the Idle Settle Down?
Intermittently. If it Starts, idles high (1400-2000), and i drive it for 10+ mins, it settles down to a high, but stable 1100-1300 RPM
Conversely, If it starts right where it should 800-900, it will creep up while driving. Ill come to a stop, check, and its back to +/-1600

The car occasionally getting it all right and it driving great gives me hope. I also desperately need to do a complete belt/pump overall as I have no clue about the last time they were replaced. 5+ years(terrifies me on the road). TBH I am struggling with what I should do next, solve this idle issue and have it running right before doing the belts? Or dont even play with the idle till the belts are good?

Sorry for the tardy reply and thank you guys for any responses!

peanut

my advice would be to not replace the belts until you have found the hard start running fault/s and corrected them first. These are interference engines and if the belt isn't aligned correctly and with the correct tension
and timing you could easily make a poor starting /running situation infinitely worse and at best you'll be adding yet another potential issue into an already crowded diagnosis situation.
When changing the cambelt and tensioners you would normally take the opportunity to replace the water pump at the same time and now the whole job has got a whole lot bigger and more expensive.!

Recommended Cam belt changes are simply that ...just a recommendation..... its not an absolute requirement. it all depends on how many miles the previous belts have done and how the engine has been driven .

My initial questions to owners is usually
1. When did it last run correctly
2. what work has been done to the car since it last ran correctly and
3. what replacement parts have been added

The answers to these questions often point towards possible areas of concern.

Question ....I notice that the car has had a Lindsay Racing Vacuum system added .....why ? was there an issue before that was added or since ?
This is where I would be looking initially because There are many components connected to the vacuum system including many non-return valves which either be could be missing or even the wrong way round . Plus there is the very real possibility that there is a leak somewhere.

As Zirconocene suggested in previous post #13
I would use a smoke test to check the vacuum system for leaks and make sure that you have all the necessary non-return valves where they should be and that the vacuum reservoir is functioning correctly .Check your Lindsay system against a 944 workshop manual diagram .

bonus12

I think it's this:
99970146840 (1 per throttle body; round seal 67.5 x 4)

Check this out. This is how I found the part number. It's my favorite source for parts diagrams and part numbers:
https://www.autoatlanta.com/porsche-...section=107-00


Your story is a familiar one! It's truly a superb vehicle in all aspects, and that includes the community here. It also includes how fun it is to asses, diagnose, and treat these cars, given the time and resources are available. As long as I've been on this forum, it's been an incredible place to seek help, offer help, and talk shop. No doubt the advice on this forum can contribute to a very well-sorted 944, and the knowledge to be a well-rounded owner.

henreezi

[QUOTE=bonus12;19544231]I think it's this:

Check this out. This is how I found the part number. It's my favorite source for parts diagrams and part numbers:
https://www.autoatlanta.com/porsche-...section=107-00


oh wow that’s incredibly useful. Thank you for sharing this

henreezi

These are great points. I already have the full set for belts/pump/thermostat/pulleys and, following your advice, will install after successfully eliminating the rough start/idle issue. Your questions are all ones I should’ve asked, and I’ll reach out to the PO for specifics. The car previously did not start before he had it. I’ll get some updates here soon. Thanks!

henreezi

Idk If I did this attachment right but this is one video of it cold starting after 3 days of sitting. This is the idle not me on the throttle. I didn’t do the things I said I would yet but am now. I’m also trying to upload another video showing the worse start attempts after this, just trying to compress it.

henreezi

TIA for any suggestions, and I’ll post an update after some tests/fixes

peanut

no video for me but the audio is perfect ,well done.
Ok ...just this second heard this and immediate thoughts are this.
Once the engine has started ,it is running fine. This tells me that there is probably nothing wrong with the TPS AFM crank and speed sensors DME and DME relay , fuel pump, Timing etc .

I think that there is 2x different issues going on here .

There is an intermittent clicking sound and an immediate momentary cutting out of the engine which is the cough you hear from the exhaust .
This is almost certainly due to something breaking down in the ignition system.

I would start by checking the ignition system first . test and check the spark plugs, plug leads, Plug caps, Coil, Distributor cap and rotor .
One test that I would try if it were my car is to start the car then pull off each one of the spark plug caps in turn from the distributor cap for 10 seconds or so and see if that eliminates the clicking sound and momentary cutting out of the engine.

The engine will run a little rough with only 3x plug leads connected which is ok as it might show you which particular cylinder is the problem.( I've added a video link below 0

If your tests do not eliminate the cutting out then you might need to substitute new parts one by one , noting any changes as you go . If a replacement part does not make a noticeable change then replace the original part again before substituting a different new replacement part .

Once you have eliminated that cough splutter, clicking ,engine cutting out then move on to the rise in engine rpm. which I believe you will find is a faulty engine temperature sensor or idle air control valve . .For some reason the idle speed is not being adjusting correctly as the engine warms up .

peanut

If you decide to remove and clean and test the Idle Air Control valve there is an easy way to do this without removing the Inlet Manifold .(see the attached video )
The other likely suspect is the Engine Temperature Sensor. If you are not sure how to test this component then just fit a new replacement.
They are cheap enough and good to have as a spare part if it doesn't cure the idle issue'

henreezi

Ok, just out of curiosity I tested my AFM by unplugging it and starting the car. I saw it somewhere on the forum and tested it real quick. Cold start it climbed up to 2200 RPM. Tried again and it was 2000. I unplugged it and it started low and climbed up steadily to 1000 and stopped. Tested again and it again climbed up to 900 and sat comfortably never fluctuating. One time it did climb high while it was unplugged. Does this suggest the AFM is compromised? I cleaned it less than two days ago. I’m not rushing to replace it but if so I appreciate any leads

im trying to find that forum but I thought he said if unplugging it did nothing you had a problem, but here it did something to mine, but it was a good result?

walfreyydo

I suggest testing the AFM
https://www.clarks-garage.com/shop-manual/elect-22.htm

I would not assume thats the issue or if its even related unless the AFM comes back faulty. Note the section about repositioning the pickup arms. Typically a bad AFM/worn pickup points exhibits stuttering and hiccups while driving (and these were the symptoms I had), so not really related to idle, but wouldnt rule it out until tested.

And apologies - I havent read the entire thread, but have you tested or replaced the DME temp sensor? Checked for vacuum leaks?

henreezi

Ok, ill try that test as well as what peanut said above here soon. It seems to be some sort of fuel-air mix issue and the Idle control valve and engine temp sensors have both been replaced (this eliminated the surging idle i had but not the high idle). Its just strange to me that when the AFM is unplugged it idle right were it should. The PO had the injectors rebuilt, regulator and coil replaced, as well as the distributor cap and rotors. Looking into common damper issues as this part looks rough. I'm still in limbo till i can get to those vacuum and pressure tests atm

"Mine went bad and I didn't notice any change in performance. Fortunately I had installed a fuel pressure gauge in the rail just beforehand. One day it changed from rock steady at idle to bouncing like crazy. Replaced the dampener and it was fixed."
-Sayporsha on another forum

Edit:
"and hiccups while driving"
it backfires like mad, not sure if this is considered a hiccup or not

walfreyydo

Stuttering/hiccups while driving is a classic symptom of bad AFM - pickup points on the contact strip become worn over 30 years creating "dead spots" in the voltage reading at certain engine loads. Requires slight repositioning of the arms. Clarks garage has the goods on what to do.