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I have just bought an '89 2.7 (78k on clock- slow steady mileage) and after less than two days of ownership it has started to play up a bit (not surprising with a nearly-30-year old car but a bit disappointing!).
Starts from cold fine (so far!)- when hot it intermittently either idles somewhere between 1100 and 1800rpm or (less frequently) it swings between 1600 and 900 in a wave-like manner.
I am still getting used to the normal noises- much less abnormal ones- so am struggling not to over-diagnose every knock and judder. The performance seems 'ok'- there is no smoke and oil seems fine.
The ICV is ticking when the power is on and throttle cable/return seems fine. I cannot easily spot a vaccum leak (my next job I think) and am aware this might be throttle body/AFM.
There is slight corrosion to the injection line from the pressure regulator (where the braided hose appears our of the rubber casing).
Help please!
In essence I am seeking some wise counsel as the to order to approach the various possible sources of this issue (partly as I don't want to cause more harm than good by just leaping in)- that and I really hate playing with fuel lines/filters etc so am hoping it is a vacuum leak!! Thanks in advance,
Hi,
With the car running and warmed up, reach under the intake manifold and unplug the ICV.
Does the idle stabilize?
This sounds like classic faulty/leaky ICV.
Another thing that can cause a fluctuating warm idle (though to a lesser RPM range) is a bad O2 sensor.
Hmm- so it's not the ICV as far as I can now tell, have also gone around cleaning the various electric contacts + looked at the air box- all fine.
I fought the brake-booster (original single piece clip) and got the clip off but failed to get the hose off the attachment (worried I was going to break the connection if I worked it any harder- will try again when feeling more brave/closer to the weekend...)- hence I have not been able to test the vacuum reliably yet. I will try with carb cleaner unless there are suggestions otherwise (was going to try smoke back from the brake boost hose).
My big issues at the moment seem to be trying to get the assortment of original clips off (a nightmare) without toasting already fragile hoses. Any tips much appreciated...
Likewise I am trying to source replacement vacuum lines but am in the UK.... ie pelican/Lindsay not ideal! Anyone recommend a UK source?
Right- have had the intake manifold off and the ICV is indeed toast + crusted with soot. I have blocked the ICV feed so is now out of the loop and car starts fine but grumbles at 600rpm for a min until things have warmed up- then seems much happier at 900.
J-boot had a crack so I have patched this whilst awaiting a replacement for this and the new ICV + have swapped out the DME temp sensor which looked aged + had a reasonable build-up of residue on the sensor probe.
The ICV I have ordered was £50 and is a 'replica' of the orig Bosch unit- it looks like new/recon units for these have really dried up recently- only one in Uk I seem to be able to buy is through design911 and is nearly £300- for a part shared with a renault 19 that feels a bit too much like real Porsche money.
Anyone know of a UK/European source for 'real' Bosch units (0280140501)? Cheers,
Ok really need some help please guys... I have replaced the ICV and has made no difference. In fact the bounce and high idle remains whether the new ICV is powered or not although (confusingly to me at least) when I isolate the ICV out of the system (powered or not) by blanking off the feed at the j-boot the car grumbles at 600 until warm and is a little bit rough but otherwise ok- then idles at 900. Pulling power to the TPS makes no difference. The car seems to have no O2 sensor (UL model and has no Cat)- ie there is a connector in the usual place at the rear of the engine bay but there seems to be a blanking plug on it (not the diagnostics port on the left)
Sounds like the ICV can't close adequately to stabilize the idle. Does it have a set screw for this adjustment? I think I have seen that on some of them. How much air can flow through it when it is closed?
Hmm- no adjustment screw and the ICV is brand new- I thought the last one was toast but as the problem has not changed with a new device I am more than puzzled - not sure about how much air flows through when closed- I can try compressing it later. Cheers m
Good question- the throttle is closing with a pleasing click and disconnecting power train to the TPS does not seem to change anything (but then nor does unplugging the ICV whereas essentially blocking it out of the system does).
The basic idea is that we want to know is ...if the DME is sensing and controlling the idle. It seems that it is not and you jumped ahead a little with swapping out the ICV. Fine but that didn't work so lets back up and go the hard way.
With everything connected and idling, adjust the air bypass screw on the throttle body- look for a little brass screw. Turn it in clockwise by a half turn or so and you should see the idle slow but then recover. I'm rusty on this but I'm expecting yours will just slow meaning no control by the DME. If true we know something in the feedback-control loop is bad.
So, now some homework... Download the WSM. Find the idle adjust procedure for the NA. find the schematic, find what the readings are supposed to be on a warm/cold temp 2 sensor. Theres always this sort of grunt work- its part of living the 944 dream. If the WSM doesn't cover it, download the DME/KLR test plan for the 944 turbo - it does cover it and the idle circuit is almost identical.
Is the DME getting good input from the temp II sensor? ... shut-off engine, check resistance through the sensor from the DME plug. Wait a few hours for things to cool and check it again.
From the TPS? Similar test, same grunt work.
From the AFM? SSDD.
and then... is the DME sending the control pulse train to the ICV? Its pretty hard to test but you can make sure the wiring is good from the DME to the ICV. And since you have an new ICV, I guess we can skip the testing of the ICV itself.
Which I think leaves you with either a bad DME or an intermittent short on one of those wires going to/from the DME. All of this is a pain but when you finally fix it you will know YOU fixed it.
And last, let us all know how its going so we can remember back to how this kicked our *** ....;] Bruce
Okay- an update and musings/seeking confirmation and advice:
Fault is still present and 944 specialist garage have been really helpful + a bit stumped- what we think is going on at present (and explains my bodge/roadkill-style fix working)- the ICV wiring loom has an intermittent defect/short just like Bruce's..... my understanding is that the ICV has been essentially open all the time (when fault present) and returning 'unmetered' air to the j-boot from the manifold- I think this is the default when unpowered too as disconnecting the pulse train to it makes no difference.
My bodge of mechanically blocking the jboot connection to the ICV and ICV hose prevented this but might be negatively impacting on crank-case pressure- although as I write this am less sure about this.
We tested the wiring from the 3 pins to dme connector and one (?33- not power) and it has intermittent continuity- esp when I wiggle the loom just in front of the firewall/under the rear of the intake manifold. The plug and wire to this point seems fine and have cut away the boot - all clear.
Does this make sense to anyone as I have now gone around with this so many times I feel a bit chicken/egg.
As a recap- TPS, DME, MAF, DME temp, ICV and vacuum all confirmed good or replaced/sorted + all connections cleaned, new distrib cap + rotors and DME relay too (but likely not related to this issue).
couple things...
- at idle air flow will always be in the direction from the J-boot to inside the intake manifold
--- a stuck open ICV would have same effect as removing the ICV altogether and just joining the hoses (suggest doing this as next test)
- idle hoses do not connect in any place to the crank vent hoses, the "feed" port for the idle valve at the J boot is several inches ahead of the port for the AOS/crank ventilation
...the ICV wiring loom has an intermittent defect/short...
A most excellent job of pursuit.
My bodge of mechanically blocking the jboot connection...
Every good hunting dog chases a few rabbits.
We tested the wiring from the 3 pins to dme connector and one (?33- not power) and it has intermittent continuity- esp when I wiggle the loom just in front of the firewall/under the rear of the intake manifold.
OK, kinda like this...
The plug and wire to this point seems fine and have cut away the boot - all clear.
So does this mean you were able to duplicate the problem but you haven't been able to actually find the break/short?
If you're able to duplicate the problem of a wire being bad, I'm thinking this might be headed for an add-on jumper wire to prove and maybe even fix the problem.... Bruce
05-25-2017, 09:02 AM
New 944 Help please- idle speed high when hot
