Flormat

Here's the whole story. Car is '86.5. I've had a failing MAF for a little while. Start up the car and for a few seconds it runs a little rough and low idle then smooths out and is perfect the rest of the day until the next morning. THen I got a noisy water pump pully so I garaged her until I got the h2o pump and timing belt changed, about three weeks. Timing belt marks lined up perfectly, checked belt tension several times, checked timing marks several times and it all looked great. Fired her up she runs VERY rough at idle and sometimes stalls and I got a couple pops out the exhaust. Rev it up to about 2000 and the engine runs smooth. So I was hoping it was just the MAF so I disconnected it. It still runs a little rough at idle but not as rough and the exhaust doesn't pop. If I bring the engine speed to about 1200-1400 or higher it is smooth. I still was not convinced if it was the MAF or if the ingnition timing is somehow off so I connected a timing light and at idle the #1 is firing at 10 degrees BTDC. Is that firing when it should? I did not disconnect any vacuum lines or anything else so that reading may be useless. Any ideas are appreciated.

jeff jackson

Did a shop do this TB-WP repair ? OR did YOU do it ? Reason I ask is..this sounds like an Ignition related problem..Did you recconect the ground wire from the driver side coil...to the 6mm Allen head screw, between the cam pulley backing plate, and the cam cover ? did you disconnect any wiring on the passenger side of the car ? Make sure all wiring has been reconnected...and is making good contact. Last but NOT least.. the connector by the ABS hydraulic controller (Large Wire..connects to a covered junction block just inside the engine bay, on the inner fenderwell, near the Driver side headlamp assembly)...was this properly reconnected ?? Very important. These subtle little electrical connections can ruin an "otherwise" perfectly accomplished belt and WP change...

Flormat

Unfortunately I must take credit for this job. I did replace the ground at the passenger side coil. I don't recall a wire at the cam cover, is that the other end of the ground by the coil or something else? And I did replace the wire by the abs controller on drivers side. I did not disconnect anything else, tried to disconnect as little as possible. Perhaps I knocked something loose. I'll go poke around a bit. And I finally found in the manuals the ignition timing should be 10 +/- 3 degrees at idle so I should be ok there. Oh and to top it off I just noticed a greasy, oily mess under my rear end. Uh... make that my transmission... pisser. Thanks Jeff.

Imo000

Are you sure you reconnect the spark plug wires in the correct order? Sound like some of them got mixed up.

jeff jackson

Yes...ther is a ground from the driver side coil bracket as well, and it terminates at a 6mm socket head cap screw between the cam sprocket backing plate...and the driver side cam cover...but...this is not likely the problem confronting you. the steady timing is a good indicator you did things right...my suspicion now is that perhaps you have a vaccuum related trouble...Is the HVAC controller vaccuum connected to the Blue-Black check valve below the brake booster ?? or someplace else ??? reason I ask is..its not at all uncommon for someone to have the small nipple on the Brake Booster check valve break off, so they plug it...and find an alternative source of vaccuum for this hose...THEN, if you have any leaking diaphrams at all in the HVAC outlet distribution system, you have a direct and constant vaccuum leak at all times..this will manifest itself most obviously when the engine is cold, or not fuly warmed....ask me how I "know" this ????

Flormat

Well I just re-checked all things. Timing marks still line up, I disconnected and re-connected the electrical connections. I replaced that brake booster checkvalve a few months ago so I doubt this is the problem but... I have at least one bad vacuum diaphram behind the console. Shortly before the WP gave it up I was noticing noise from one of the vacuum diaphrams... that would give me a vacuum leak bad enough to cause the problem I am having now?!! Thanks, Jeff.
Imo000, I never disconnected the plug wires from caps so that shouldn't be a problem but still a good thought, thanks.

jeff jackson

Check all the groundpoints...make sure they are clean and tight. Then install a vaccuum gauge with a splice into the vaccuum line that feeds the fuel pressure damper at the front of the motor, and see what your car is doing for vaccuum during the rough operation...at idle, you should have at least 18" of vaccuum. if NO...then you have some detective work to do...good luck. PS, the vaccuum gauge that comes installed on the Mity Vac tool just unscrews from the tool, and splicing some rubber vaccuum tubing into the line that feeds the fuel pressure damper and connecting it to the gauge unit only takes a moment to do...and will tell you much about the nature of the problem.

Flormat

I did the vacuum test on the fuel pressure damper but I didn't have a "T" fitting to splice in the gauge. Instead I connected the fitting on the front of the MityVac to the vacuum source and the top MityVac fitting to the fuel pressure damper. I also reconnected the MAF. The engine is cold so it was hard to get it to idle- just wanted to die. When I could hold it at idle the vacuum gauge registered just above zero, about 1 or 2". At around 2000 RPM is would register at about 5", and at 3000 rpm it would register about 13 or 14". If the way I connected the MityVac works then that is some serious vacuum leakage. But why would it run a little better with the MAF disconnected?
Now I can't help but wonder... when I parked the car a month ago it ran fine. And now there is a large puddle of fluid under the transmission. Doesn't the transmission get vacuum? Could the tranny puddle and this low vacuum issue be related? Thanks again, Jeff.

Flormat

I did some vacuum testing of the components today. The black line coming from the blue/black check valve off the brake booster is leaking VERY badly. Also the blue/black check valve is leaking. Another component that won't hold vacuum is the Control Valve II, part # 928 110 429 07. That control valve's vacuum line is connected to five other parts as well such as fuel pressure regulator, both fuel pressure dampers, transmission modulator, and something else. So if the fuel pressure regulator is not holding vacuum would I get a lean mixture? If so that might make sense that by disconnecting the MAF it runs better but not perfect because if I'm not mistaken that gives it a rich mixture?

jeff jackson

FIX these vaccuum issues...should NOT be difficult, now that you have pinpointed the necessary items,...then worry abot where do you go from there...MeThinks...this alone..wil make a HUGE improvement in the cars performance...

jeff jackson

Flormat..make sure the "O" ring seal..where the MAF slides into the throttle housing..is intact, and sealing properly. Also...there should be a large diameter, but very thin "O" Ring..around the base of the MAF itself (where it slides into te throttle housing)..lubricate both of these "O" Rings with a silicone based lubricant, and make sure all the vaccuum hoses and fittings are in good condition. Look at every one of them. Thsi vaccuum issue is SERIOUS..it cotrols the fuel injection system to a level that can result in disasterous consequences..if not promptly rectified... Hae youhad the Intake Manifold off the car for any reason at anytime prior to the problems you are describing ??? If SO..then you may need to start there as the culprit for the vaccuum readings you are observing. FRANKLY..I am surprised, the engine would run AT ALL...with this kind of available vaccuum. At this point, I think it best to "defer" to some of the regular "wrenches" here on the board for proper advice.

Flormat

No I haven't had the intake manifold off ever. Maybe just sitting for a month is all it needed to become the problem it is now. I'll have to order some parts but I'll let you know what I find. Thanks Jeff.

borland

I believe that during the cold warmup period, the O2 sensor is disabled, so all of the metering is by MAF.

A marginal MAF could provide the symptoms you describe. But the wide fluxuation of idle speed during warmup is usually a bad idle stabilizer valve.