87 Turbo High Idle after warmup

[mdripley]

This is my first post on this site. I have an 87 Turbo 930 it has 80,000 miles.
It has just started to be slow to start idles very slow 500 RPM until warmed up.
It then Idles at approx. 1800 RPM. It also bogs down when trying to accelerate.
Once it is fully warmed up it will Accelerate very well for a short period of time then starts to bog down again. it pops and shakes abit while idling. and feels like it is missing abit. TIA for any suggestions I will be following the factory trouble shooting charts and metering all of the items listed to be checked.

[j930]

WUR maybe? a place to start.

[HFR_Racer]

Sounds like you need to dive into the diagnostic stage of owning a 930

High idle after warm might be a sticking IAC valve. Might be sticking mechanical advance weights in the distributor. Popping and shaking may be a vacuum leak. Maybe you recently changed your plug wires and mis-installed? Maybe you've got a burnt resistor in an ignition wire causing a my-fire. Maybe you have cross-firing?

Bogging down during accel does sound like fuel..


Does the mis-fire get worse as rpm increases?

Please provide more detail on the service history. Ever changed the fuel filter? Plugs, wires, cap, rotor?

Any recent engine work that might've led to you issues? Had the IC off, etc???

[mdripley]

This car was purchased new by my Father, he was the only owner until he passed away Jan 2012. The car came complete with a full service history. It was well maintained until he died. The car sat for 8 months in the garage of his estate until I picked it up this last august. I have changed the oil, Oil filter, fuel Filter, Air filter. This car was running fine being driven 1200 miles since August. It just started to act up now. the bogging occurs while Driving during acceleration it bogs down immediately. The popping occurs mainly at low speed or idle once warmed up.

[mdripley]

I was planning to take the car in for a check up, but want to troubleshoot the problem first.

[mark houghton]

First of all, it shouldn't idle at 1800 rpm when warm, and it should idle higher than 500 when cold. If the AAR were stuck open, it would idle high when cold, then even higher when hot. So deduction says it's not the AAR.

Might be that it's running too lean across the board, pointing to 'perhaps' the WUR but more likely to an air leak somewhere. Or might be that the airflow/fuel metering arm is gummed up and not moving down enough in response to air flow...which would cause a lean condition when stepping on the gas. You would have to pull the air cleaner assembly off the fuel distributor and depress the metering plate to see how it's acting.

The popping and rough idle may point to ignition...perhaps as simple as a pulled plug wire or a plug that's beginning to foul and is fine until you put a load of fuel to her and she misfires. Wash the car lately? Check inside the distributor cap for moisture and/or carbon tracks.

Could be this, could be that...so difficult to diagnose from afar. We're good at sending folks off on goose chases and there are a zillion places to look, but a person has to check all things in order to find the culprit. No doubt you'll spend hours dicking around before you find that 'ah-ha!" moment. If you have the skills, tools, patience and perseverance then start looking first for the obvious. Or limp her in to your favorite wrench to do the work.

Or maybe...in the words of the immortal Bonnie and Clyde, it could just be "dirt in the carburetor...I just blewwed it way!" (or is it just me that remembers that line?)

[totle]

An easy check to verify AAF is to use a wise grip over the hose between intercooler and AAF. This will block air flowing towards the AAF, and If AAF is not closing properly idle will go down.

As Mark points out, could be an airleak somewhere.

[mdripley]

Thanks for all of the tips, I am just waiting for it to warm up alittle more outside so I can feel what I am doing while trouble shooting.

[kevinkjse]

Hi I Put my turbo away for winter in my warm garage, was running great before it went into hibernation, got it out for an mot and thought good excuse for a run.

Not good, does not want to run above 0.4 bar looses all power and blows black smoke also the tick over is now some 1800 rpm, I know the on board bar gauge can not be relied upon but seems to get up to 0.4 bar too quickly, seemed to clear for a few seconds but now seems permanent!

Found it thanks to a phone call to Bob Watson, Relay for Fuel Pump No.2 Item G

Now running like a dream!
Indeed very strange. I am sure someone on here will explain it a lot better than me but Bob said the 2 x fuel pumps are needed to boost the fuel pressure to around 6 bar, roughly 90 psi which is quite a high pressure and if you loose 1 x pump the pressure drop causes all sorts of symptoms, still will fit 2 x new relays and job's a gooden.

kev

[T77911S]

could be a big air leak. did you remove the intercooler? make sure the advance and vacuum diaphragms are working on the dist.
check fuel pressures
how about power to the warm up regulator (WUR).

i/we do not know how familiar you are with porsche's, but just wanted to add since you changed the oil, you do know to check the oil level with it idling and hot?

[mark houghton]

Originally Posted by kevinkjse

Hi I Put my turbo away for winter in my warm garage, was running great before it went into hibernation, got it out for an mot and thought good excuse for a run.

Not good, does not want to run above 0.4 bar looses all power and blows black smoke also the tick over is now some 1800 rpm, I know the on board bar gauge can not be relied upon but seems to get up to 0.4 bar too quickly, seemed to clear for a few seconds but now seems permanent!

Found it thanks to a phone call to Bob Watson, Relay for Fuel Pump No.2 Item G

Now running like a dream!
Indeed very strange. I am sure someone on here will explain it a lot better than me but Bob said the 2 x fuel pumps are needed to boost the fuel pressure to around 6 bar, roughly 90 psi which is quite a high pressure and if you loose 1 x pump the pressure drop causes all sorts of symptoms, still will fit 2 x new relays and job's a gooden.

kev

Here's' a rough description: The high system pressure puts "tension" against the metering plate arm assembly, giving it resistance against which to move as the engine pulls air across it. That's how CIS works, the arm deflects in response to the air flow and as it deflects, it injects more fuel.
With only one fuel pump running there is less resistance, so the arm moves easier than it should and injects too much fuel (thus your black smoke on boost). And once you get the rpms up, the single pump isn't enough to supply the volume needed either. These cars will run with a single pump but poorly as you've discovered.

[kevinkjse]

Thanks Mark

Very well put!

regards

kev

[mark houghton]

Originally Posted by kevinkjse

Thanks Mark

Very well put!

regards

kev

I may not have been 100% accurate, but system pressure changes should also have an impact on control pressures....and in reality it's the control pressure that the WUR sets up which determines how much the control arm moves in response to air velocity. I have a rudimentary understanding of the CIS fueling (enough to get me by, or get me in trouble). I could name a couple of folks here that know it intimately, and they know me well enough not to shy away from corrections!

So many people don't understand that with CIS, the lower the control pressure - the richer the mixture. If you internalize just that one piece, a lot of stuff starts to make sense.

[mdripley]

Thanks for the additional information. I have not yet gotten the chance to troubleshoot the issue yet, As I must work to afford this great car. once I have it cleaned up and back in tip top running condition I will post some pictures, and I will maintain a log of the steps taken to remedy the current problems. For a car this old It is in better shape than I expected.

[heliolps2]

Maybe I can help with this , call me at 210-473-7158 it's easier to explain over the phone,

[mdripley]

I wish to thank everyone that gave me suggestions on what to check to resolve my issues. I have resolved the issue it was due to one of my relays being bounced out of it's socket. and all the others were just about half way out of their sockets. I have reinstalled the relay that came out of it's socket and reseated all of the remaining relays. Now this baby is running beautifully, it idles at 950 still just a little fast so I will continue checking all lines, hoses, Seals, etc. I will also be replacing my Dizzy cap and rotor, Spark plugs, possibly the wires as well. Tomorrow I will be replacing the intercooler seals. And once my valve cover gaskets get here I will adjust the Valves. Once again Thanks to everyone on this board. My sled to heaven is back.

Mike

[mdripley]

Found out today that the Air Flow Sensor Boost Pressure Relay is gone and a set of jumpers are plugged in the relay Recepticle( engine compartment panel). Why would someone Jumper that Relay? What possible side effects could this cause? Well I will order a replacement after checking for other possible rigging or bypassing.

[mdripley]

Gotta love that sticky on no starts, answered all my questions about the missing relay.

[kevinkjse]

Which relay had fallen out, fuel pump 1 or 2 maybe ???

[mdripley]

The number 1 fuel Pump Relay fell out.

Mike