1990 Q45 Need help to diagnose....

[pito11213]

Ok fellas here it is..

Put the scanner on my Q and came up with a bad knock sensor on bank 2 reading lean only.

The Q has a horrible bouncy feeling when you just leave it at idle in park or drive. When you hit the accelarator at 2000 rpm there is a pronounced vibration. Now this symptom since I have had it in NY has been on and off but now it seems more consistant. I have cleaned the MAF thoroughly and replaced the fuel filter. Also sprayed the throttle body with 1 and a half can of throttle body cleaner and two bottle of BG and two of techron.

Now when we hooked up the scanner it read the injectors at idle pulsing at 2.45 and up to 2.46 fluxuating. Now it shows by bank so are these numbers about normal?

Now for the biggie....My timing at BTDC was at 8 - is this normal or correct?

I want to do a power balance test to get those results also.

I am just frustrated right now as I have considered engine replacement but with the price of that plus all the miscellaneous I could have the price of another Q. But I like mines and since it is mine I would like to keep it.

The car runs like a bat out of hell it is just when you are at idle that the shake is there. You can actually see the car bouncing...very annoying.

All suggestions and data is welcomed.

[911/Q45]

Just about has to be an injector, have you done the ohm test on them?

[Bwana]

I'm thinking injector as well. Though there's the outside chance of a bad plug...

[Q_SHIP]

Mine was doing the exact same thing. At idle it would bounce and the miss got very noticable at 2,000 Rpm. Replaced injector 5 and is was gone. I would be 99% sure thats your issue.

[DAEDALUS]

Base timing is 15*, 8* is way off. A bad injector would lean things down, a bad plug would richen things up, suggesting an injector problem. Pulling the #2 bank plugs might give some clues, but easier to ohm the injectors if it's out electrically.

[pito11213]

ok

The weird thing is that it does not feel or sound like a miss. How about this as a possibility....bad spark plugs. Bottom line the car has not had a tune up in atleast 2.5 years. Nothing at all. I was thinking of changing the plugs and doing the seafoam. What do you think? Also at the same time I would ohm the injectors.

[Jesda]

I'd grab a meter and ohm the injectors before doing anything else. Probably overdue for plugs anyway.

[elwesso]

Your timing is so far off, with bad injetors. Youll wet yourself when your Q runs right...

Just ohm injectors sometime soon..... Dont wait, sooner is better than later.....

[ScottJackson]

Ohm those injectors thru the harness on the passenger side rocker cover. If that checks out fine, my next step would be to look for vacuum leaks. The best thing is to start the car and use an UNLIT propane torch and fan the propane gas around all the vacuum hoses, intake, throttle body... anywhere you could have a vacuum leak. If the engine speeds up and evens out, you found the leak. I commonly use a can of carb cleaner and spray it around areas for the same results. One unlikely spot to check for vacuum leak is inside the car behind the brake pedal where the brake booster is.

[Q451990]

If you have an injector issue, the plug on that cylinder will probably be fouled. You might make sure your injectors are good first so you don't replace the plugs - only to foul one again. It is very unlikely that OEM plugs could fail to the extent that you would have a miss. If someone used aftermarket plugs (especially Bosch +4) then it's a possibility.

Heath

[Q451990]

Put the scanner on my Q and came up with a bad knock sensor on bank 2 reading lean only.

The knock sensor doesn't read lean vs. rich... do you mean a knock sensor and an O2 sensor on bank 2?

Heath

[DAEDALUS]

I assumed the scanner was giving codes and showing rich/lean for the O2 sensors. Plugs unlikely, but it could be a bad coil too.

[pito11213]

So many possibilities but the general thing I guess is to start with ohming the injectors. I will have to do that first.

I really cant say that it is a miss because it drives like it is ok. When you put down the accelarator it spins the tires no problem. It is just when sitting there that the bounce it profound.

I believe it said code 34 knock sensor

Ill check again at the end of the week.

So do you guys think a seafoam treatment is warranted?

[Jesda]

You know whats odd, is I'm having the exact same problem, but after using Seafoam it will be fine for 2-3 days (and the problem will come back).

If its an injector problem I'm having, how is it that seafoam is temporarily resolving the symptom?--I'm going to pick up a meter and see which injector is giving me trouble. Acceleration is getting rough, idle is bouncy, and the vibration is driving me mad.

-Jesda

[Q451990]

The car still runs strong on seven cylinders - but that bounce sure sounds like a dead miss to me. Jesda - when you say SeaFoam, are you running it in the gas tank as an injector cleaner?

Heath

[pito11213]

Jesda I feel your pain (literally)

Q90....I am pretty sure you are right and when i get to the ohm test that will be the tell all.

[Jesda]

The bouncing effect I get at idle is minor, but noticeable. The longer I sit at idle, the worse it gets. After a long highway drive it isnt there at all. Im running seafoam through the brake booster.

[pito11213]

Yeah my bounce is noticeable also that is the problem it didnt do it before. I was thinking of trying new plugs with seafoam in the gas tank,crankcase and brake booster....What do you guys think. Of course this would be dependant on my ohming of the injectors

[elwesso]

I think Jesda's shake is due to imbalance. Dirty injectors and VERY dirty plenum... Pito if you hvae blue smoke you are gonna have TONS of blowby and the plenum is probably unreal..... My Q has a less than stellar idle as well, and i think i need to clean maf and bg44k.....

I drove a Q with 2 bad injectors, bad KS, and dirty KS, and it still runs surprisingly good.....

Dont seafoam, you treating the symptom not the cause.. Live with it then it iwll remind you to fix!!!