Rough idle/no rev problem
 

I'm going to move this problem to the technical forum. I have a '98 Boxster Base with a rough idle/no rev problem. The battery and plugs are new. The coil packs ohm out. The fuel pump and fuel filter are new. Fuel pressure is rock solid. The vacuum looks to be good. Oil has been changed as well. Could a stuck fuel injector or injectors cause the rough idle and inability to rev about 300 rpm?

I'd check your MAF. I had similar symptoms and it turned out my MAF had failed.

I second the maf. If you disconnect the maf sensor the engine should then run in open loop. If it runs better it is a sure sign the maf is bad. Sometimes cleaning them helps but not always and be sure to use a cleaner spray designed for maf cleaning

Disconnecting the MAF made no difference. I am definitely missing on cylinders. Trying to get access to ohm out the injectors. From underneath it's tricky. May have to remove the secondary air pump on the passenger side and the air box on the drivers side to get full access to the injectors and rail.

A major vacuum leak would cause this. Are you getting any codes?

No codes at all. No CEL as well

Does anyone know the proper resistance for the injectors? I got to one and measured 12.2 ohms. I also measured the voltage at the injector connector to be 12 volts with just the key on.

Have you checked for vacuum leaks? I had this happen after doing some work on the intake. Put it back together and couldn't see it from the top, but I had created a vacuum leak when I put it back together wrong. No codes because it wouldn't stay running. If you aren't getting any codes I highly doubt it's anything related to your injectors.

Thanks for the replies. I would really like to learn a way to check this vehicle for vacuum leaks. I have checked the vacuum lines on the drivers side that goes to the fuel regulator. I can see no leaks and fuel pressure changed when disconnecting the vacuum line. On the passenger side, I have traced from the intake manifold all the way to the vacuum canister and the four way tee. I can't see any damage to the lines so far. And I can't really do much other than visual inspection. Pin hole leaks would be almost impossible to detect visually. And I can only keep the car running about 15 seconds, so chasing a leak with something like carb cleaner won't work. Keeping it running long enough to troubleshoot is a problem. I'll post a video of it running to give you all a better idea of what I am seeing and hearing. I do appreciate all of your help.

Here's a video of its normal performance:

Boxster kind of running photo, picture, image on Use.com

You can rent a smoke machine, make your own, or get it to a mechanic to figure out. This is the best way to check for vacuum leaks...with only being able to run for 15 seconds, it isn't a small leak or a pinhole issue if it is caused by a vacuum leak.

When was the last time the car ran right? What have you done to it that may require you to check your work? If you retrace those steps you may find the answer.

It never ran right, yet. In other threads in the General Discussion area I explained I bought a non runner and am trying to get it going.

I haven't heard of these things having much of an issue with injectors. I'd look into a smoke machine to get that at least eliminated as a cause. After that I'm not sure where to lead you with no codes being posted.

Brake boost vacuum line? That's the biggest one and I'd think most likely to completely stall the engine. It mounts to the front left or right rear intake manifold and the opposing one should be covered/blocked.
http://986forum.com/forums/uploads01...1458511868.jpg

Mine ran like that when I left the oil fill cap off. It creates a vac leak. Worth checking the cap and the fill tube.

Last two posts are good examples of why I'm saying try and track down a vacuum leak. The car will tolerate them for a bit but when they become too large it can no longer compensate and it shuts down.

Thank you all again for advice. I'm going to do some disassembly tomorrow and track down that leak. Took the day off and went down to Tubac, AZ (a small artists colony). Bought a couple of pots for my wife and had a great Mexican meal with my wife (the margaritas are hampering car repair). The goal is to have the car running by my 33rd anniversary at Memorial Day and drive it to San Diego.

I took a look this morning and found this, should it attach to something?

That looks like the power steering overflow hose. It doesn't attach to anything.

Thanks for the quick reply

Oil filler cap
 

If you have the orange oil fill cap, try replacing that. I had similiar issues, not as bad though. Original oil filler cap would not tighten all the way, causing air leak. Sometimes suction of engine running would pull cap tighter, making a seal - this made it harder to track down the issue.

I bought a new oil fill cap that is very tight, and it made a huge difference in how the car runs - feels like a new engine!

Good luck!

Went on my search for the vacuum leak. Still no apparent damage can be seen as I traced past the vacuum canister. The brake booster connection looked good too. But the oil cap mentioned above concerned me. So I got her putting along and removed the oil cap. I saw no difference in performance. So I traced the oil filler tube in the engine compartment. But I couldn't find any damage, cracks, or oil leaks. Can this filler tube (any of the three pieces) or even a bad oil cap (mine looks yellow) cause a massive vacuum leak? Thanks in advance.

When you remove the oil cap, you loose all the vacuum and the engine will run crappy… :rolleyes:

Buy a new oil cap. It's cheap and yours is an old part number. Search this forum for how to make your own smoke machine or rent one. I'm telling you if you're going to check for leaks, do it right. Smoke goes into the intake and it comes out where your leak is. Couldn't be easier. Yes the oil fill tube can be a big one. They are plastic and can rip wide open. Hard to see without a smoke machine.

Ordered the oil filler cap. Got everything together to build my smoke machine tonight. I didn't realize that they are basically a vaporizer with a regulated air input. I'll remove the MAF and clean it while I have it out. Thinking about using the hole where the MAF is located to inject the smoke, sealed by a custom gasket (duct tape). Then I can finally see where this car is leaking. Will post some videos of it.

Smoke Machine
 

I made a cheap smoke machine and tried it out. Ran out of time to smoke the engine. Here's some pics and a video

https://youtu.be/P5t3gg4ghjI

A pic of the coil and wick smoking

Nice work tada! Let us know how it works out! At least now you'll hopefully be able to cross vacuum leaks off the list

I do have some questions about performing the smoke test. I am assuming that smoke will escape through the air filter box. Is there a way to plug it up without full disassembly? Also, do I need to hold the throttle open while testing? Thanks in advance

You can use some of that special gasket material on the outside intake.

The closed throttle will most likely block the smoke. Introduce the smoke into one of the tubes that comes off the Y connector near the vacuum reservoir - or at the fuel pressure regulator?

Well, ran the smoke test with no luck. I performed it pretty much like the Pelican write up. I removed the MAF, cleaned it, set it aside. I sealed off the snorkel and air box cover. Then I pumped smoke in. I have a video, but it's pretty bad. Anyway, went in through the MAF opening (sealed off) and smoke was being generated. But I saw no leaks at the throttle body, the brake booster, the tiny fittings, the canister, nowhere. I then held the throttle body open, hoping smoke would pass farther. Still no leaks. And I opened the oil filler cap. No smoke would ever reach it. But putting smoke in through the intake wouldn't really generate smoke from the filler tube or crankcase unless the PCV valve was bad, would it? So I put the smoke directly into the oil filler tube and sealed the top. No leaks in either of the three sections, the crankcase, or where the middle tube attaches. So I can find no vacuum leaks at this point that is causing the crappy idle and stalling. But it was a fun test to try. Any ideas? Did I do it wrong?

So to summarize, a non runner bought from a PO who bought it from a dealer in July. Stored in a garage over winter, would not start. He changed the plugs and what looks to be the ignition switch. I jump started it when I inspected it and it runs as seen in my video. I replaced the battery, fuel pump, fuel filter, fuel sending unit, and plugs. Changed the oil. It was brown not black, no metal found in oil or filter even using magnet. Coil packs ohm out ok. Injectors ohm out as well. Now, no vacuum leaks. I'm now wondering about the DME. Or maybe carbon build up in the throttle body.

An update
 

I stepped away and tried to think about this. I found the plugs in cylinders 1, 2, and 3, which have no miles on them to be covered with soot. So I smelled the oil dipstick and found it to smell like gasoline. So, I replaced the fuel pressure regulator. The result was the same, rough idle, missing, dies when given any gas. But it does run longer now. Also some white smoke came from the exhaust. So at this point I guess I move on to the injectors and a lot of disassembly to get them out. While I'm removing pieces, it should be an excellent time to clean and check every fiddly piece for leaks. Any advice or encouragement would be appreciated.

At minimum you will have to either clean your plugs or get new ones since they're fouled now. Are you sure the proper plugs have been installed by PO? Electrical issue maybe as injectors are working but no plugs firing? Sounds like plenty fuel there. Once plugs load up they are hard to fire.

I replaced the plugs with Bosch platinum plus 4 plugs. But I have read some bad reviews of them since. I'll get some new plugs tomorrow and go with original OEM to see if that changes things. I'm also going to clean the throttle body and intake air control valve. Thank you for the suggestion on spark plugs.

Probably a really dumb suggestion. But since you bought a non runner, did you completely drain fuel and add new fresh? Might be worth trying some chevron tech Ron in the tank if you can get it to run long enough.

No, very good question. Since I bought it, I replaced the fuel pump, fuel filter, fuel sender, and fuel pressure regulator. Installing the pump meant draining the tank. While in there I cleaned it out completely. It now has 5 gal of Shell 91 octane gas and a full bottle of Techron in it (6 for $19.99 at Costco). So other than the injectors, I feel pretty good about the fuel system. But when it runs, I don't smell gas - just exhaust fumes. It's hard to get a stethoscope on the injectors for the 20 seconds it runs. But it sounds fuel starved still and I wonder if an injector stuck open or closed could cause this?

I've also got a real Durametric arriving next week to finally get some real data on this car. I've been using an iCarsoft POR II and it has been nothing other than a basic OBD reader to me.

Oil pressure switch?

That's an interesting idea that made me break out the Google machine. I do have a slight oil leak that is not the spark plug tubes (replaced), not the camshaft plugs (replaced), not a RMS leak, and appears to be coming from under the passenger side air plenum. So as I understand it, there is a oil pressure/temperature sensor under there next to a knock sensor. But doesn't that just drive the gauges and send info to the DME? Would it really cause the idle/stalling problem?

My thought is this, low oil pressure is locked out for start up, but I believe times out if low pressure does not clear in specific time. This may shut down the fuel pump. This is typically a safety system so if car gets in wreck and catches fire the fuel pump doesn't continue running. Just a thought.

It's a great idea. The part is cheap. Access is a pain, but removing the intake manifold for cleaning may solve that. And if it is leaking, I'd like to correct that. Thank you!