KandA928

Good morning 986 crowd. I'm new to this branch of the forum. I have recently picked up a pair of 986 cars but usually play with the 951s.

Big question: Is there a difference between 1997 ECU/DME/Immobilizer and 98-99 units?
My 97 2.5 5 speed manual car recently had body drain issues resulting in a fried immobilizer. Then the car was dried out and drains fixed and the car sat for 6-7 months.
I replaced the Immobilizer, DME and Ignition switch (98 or 99MY matched set) and it started and runs, albeit having a stuttering problem.
I have a trouble code thrown now for a purge vent valve. The gas could also be bad as it wasn't driven often and has sat for months now.

The replacement ECU,Imm,DME, Ignition switch came from a 98 or 99 car. Could this be the problem?. I located the carbon canister and it doesn't have a Vent Valve, or and electrical connection to connect one

Is there a difference between 98-99 vs 97 ECU units that would cause a fake Engine control light? Or any other known incompatibility issues?

Any insight would be greatly appreciated.

Macster

If you managed to swap the ECU, IMM, DME (same as ECU?) and the ignition switch from a '98/'99 car into a '97 car and you are able to unlock/lock the car, start the engine, that's a pretty good sign there are no significant differences between those items and the MY's you listed.

The CEL is on because there is an emissions related problem and the finger is pointed at the purge vent valve. My advice would be to do a search using the error code and see what others have done to address the cause of the error.

The gas could be, almost certainly is, stale. My limited experience with 6+ month old gas in a new Infiniti is the engine still started and idled just fine, but the engine was a bit flat. This was made obvious to me after I had driven the car enough to burn up the stale gas. After filling the tank with fresh fuel the engine was transformed.

In the case of the Boxster the condition of the gas might account for the "stuttering" but also so could the problem that triggered the CEL.

I'd take care of that first. After you eliminate the CEL then if the engine still stutters you can deal with that.

As an aside, any time a vehicle sits for any length of time, there's always the risk of rodent infestation and damage. You probably should inspect the car very carefully for rodent sign: bare patches in the carpet, signs of gnawing on rubber/plastic lines/hoses, trash on top of the underbody plastic panels, etc.

KandA928

Hey thanks for the reply. I agree wholeheartedly on the fuel. Went ahead and sucked the tank clean of the old fuel, added 5 gal of fresh 93 and some StaBil for ethanol enriched gas.

My carbon canister is missing the canister purge valve...but the main culprit of my stuttering woes is an Air Oil Separator that is allowing oil to be sucked in to the intake at far more than the recommended dosage.

My fingers are crossed that the updated replacement part and Pedro's replacement procedure with be a fix.

I will certainly remove and clean the intake pieces and hopefully haven't gotten a fouled MAF....

Anyone have a quick link that details this teardown a little more completely?

Andrew

Macster

I've been through 3 AOS's with my 2002 Boxster. The AOS lasts around 80K to 100K miles. (The car has just over 296K miles on it.) Each and every time I just have the tech install the standard factory AOS. The part is ot very expensive -- the Motorsports is very pricey -- and doesn't take much to install.

The first AOS failure I was all worried about the intake being oily the plugs being oily the exhaust being oily and was going to have the intake removed and cleaned, the plugs changed, and the exhaust removed and flushed with solvent but the SM at the dealer talked me out of all this. Said it wasn't necessary. It wasn't.

The 2nd and 3rd failures I just had the AOS replaced and drove the car. Any oil in the intake or on the plugs or in the exhaust burns away pretty quick.

The MAF is far enough away it doesn't get oily. I never clean this.

My advice is do not delay getting the bum AOS replaced. The risk is of too much oil is ingested by the engine and this can lead to hydraulic lock of the engine with possibly fatal -- to the engine -- results.

It is kind of tricky... The engine may be ok running, but shut it off and leave it sit. The intake is drenched in oil and this drains down and through an open intake valve and the next time you go to start the engine the cylinder is full -- it doesn't take much to fill the space when the piston is at the top of its compression stroke - and the engine locks up.

There are I bet a number of articles on how to replace the AOS. You might try the Pelican site. It has a pretty good selection of DIY articles in various Boxster servicing and repairs. Also, I think the Porsche Boxster Service Manual by Bentley covers this repair. If you own a Boxster you should get this book.

KandA928

986 guys, I'm having a little trouble still with a 1997 Boxster.

Recap. Bought car with Immobilizer damage. Replaced Immobilizer, ECU and Ignition switch. Car now runs....at idle. Drove 1/2 mile and got some stuttering on throttle above 2500rpm (old gas, I thought) Put the car on my trailer and it started stumbling, stalled going up the ramps.(Nose up) Since then, it won't idle or stay running.

I drained the fuel from the tank, replaced with fresh gas and stabil.

I Checked AOS vent tube, oily.
So I Replaced the AOS with the updated version, Removed the intake and throttle body and cleaned the oil from the center section in between the two intake manifolds. No real oil in the intake manifolds when I wiped them out

No Change. Car will start, then stumbles and won't idle. Won't pick up on throttle either. A little popping/misfiring when you try the throttle. Sometimes will catch and rev to 3 or 4k on the tach but then stumble. Tapping the throttle lightly I can get it to stumble on roughly but not idle. Runs smoothly when a little starter fluid is sprayed in the intake....(IE no stuttering or shaking as if 1 or more cylinders aren't firing)

Replaced Fuel Filter. Still no change.


Should I replace the fuel pressure regulator? Should I check the fuel pump itself?

Any suggestions for troubleshooting?

evifenocvt

you probably need to swap out the purge valve thats on the gas filler pipe. valve has an orange tip that connects to the evap hose. or its possible that your charcoal canister has a hairline crack. both can cause a small evap leak code, as well as bad gas cap.

id also check all your wiring in the engine bay. if it sat untouched for so long, some rats might have nested in there and gotten to the wires.

Macster

Could be any number of things. evifenocvt covers some.

Reads like a lean condition. Thus suspecting fuel supply or pressure is reasonable.

However, I like to keep in mind the last thing touched is the first thing suspected. These cars are getting old. Hoses and plastic fittings and connections and wiring are all getting old, too, and fragile.

Thus my recommendation would before you throw any parts at the behavior would be to double check your AOS installation and all the hoses/lines/etc for any damage which can be a leak.

While you are at it check for any signs of rodent infestation. I have seen them gnaw on the engine wiring harness, through the heavy rubber that makes up the radiator ducts, scrape carpet fuzz from the carpet and gnaw through the vapor vent line that runs from the tank to the engine compartment. This line is hidden behind the plastic underbody panel or can be at least was in the Cayman that I saw on the lift with this damage.

Before I go on I'm reluctant to encourage a DIY'er to mess with the fuel system. Fire is always a possibility. (Not too long ago a guy working on his vintage car -- some older Camaro model I think -- the engine caught fire and destroyed the car, another car parked next to it and damaged the garage.)

My advice is to have a professional auto tech do this work.

You can check fuel flow and pressure.

Be aware there can be fuel pressure at any line you open so have a rag handy to wrap about the line and catch fuel.

Also, please note that in checking pressure the brass cap that seals the fuel pressure test point is not reusable. You have to replace this with new. Engine off pressure is 3.8 bar +/- 0.2 bar. Engine idling fuel pressure s/b 3.3 bar +/- 0.2 bar.

Pump should flow 0.9l in 30 seconds. This is measured through the fuel return line.

Keep in mind the fuel pump might be ok it can be the fuel pump relay. A fuel pump bypass relay -- for testing purposes -- can be bought at the Porsche dealer parts department. I ordered one but when it came in the parts manager said someone else was wanting one in a hurry and would I mind giving it up to this other person? I said I wouldn't mind and one of the techs in the service department loaned me his test relay to use. In the case of my Boxster the relay was ok, it as the fuel pump that was bad.

KandA928

Macster, evifenocvt Thanks for the input. I took a few steps to try to solve it based on your input.

1. I went back through after my AOS replacement and felt confident that my connections were plugged in. FYI, The AOS design was changed between 97' and today a couple of times, so anyone doing this update will need the updated hard hose between the AOS and intake as well.

2. My Idle stabilizer was fouled from the oil supplied through the faulty AOS. I cleaned it, as well as the intake tubes. I felt like it was still a bit sticky internally, and I ended up swapping in a known good stabilizer valve from my spare motor. The car still didn't idle, died.

3. TPS, I had a spare TPS as well, why not? Still no change in behavior.

4. MAF!. I bought a replacement MAF sensor and installed it, and now the Car runs great. Found it cheap for $23 using a google search.