'92 525 11mpg, rough idle, 1222 code

[wilkie3]

I change my fuel filter and my fuel economy has gone down. I used to get around 17mpg in the city with the air off, but now I get 11mpg and a 1222 error code when I idle.

I changed the O2 sensor and plugs last summer '04.

I have read the forum threads on this subject, but I am not sure why my fuel economy has dropped so far. I hear a distict hissing sound when I put my ear on the intake manifold. I am assuming this is normal.

I also checked the brake booster vavle and the extra hole is plugged.

Any ideas, please?

Thanks

[SRR2]

"Hissing"? In a car this age and usage you can expect the rubber in the induction system to be hardened and cracking. You'd better start looking for cracks, and that hissing sound should be the place to start.

[632 Regal]

also do a reboot, the car is running in safe mode. The O2 sensor will be triggered from a miriad of other things such as vacumm leaks.

[wilkie3]

1. What is a good way to locate my vacuum leaks?
2. So a hissing sound in the intake is not normal?
3. What mileage should I be getting, in general?

I performed a reboot, but no change.

Thanks.

[tim]

Inspect the plastic boot from your air filter to your intake. Invariably, there's a big crack on the underside where you can't see it from above, and it's letting in alot of unmetered air. 1222 is lambda, so there are only three possible variables- gas, air, and o2 sensor.

Oh, by the way, just because that o2 sensor is newish doesn't mean it works, especially if it was one of those 2 wire "universal" dealies.

[tim]

I had another thought: you say you changed the fuel filter- it is possible to install it backwards by mistake (no offense to you- I've done it myself). It seems counterintuitive based upon the low mileage symptom, but hey, you never know. On yours, the arrow should point towards the driver's side.

[SRR2]

You're going to have to disassemble that plumbing to be sure you're finding all that bad parts. Fortunately that disassembly isn't at all difficult. If I were in your situation, I'd probably just buy new rubber parts for all the intake (everything past the MAF, and including crankcase ventilation and ICV plumbing) and be done with it. At your car's age and mileage, they're all going to be hard and crack-prone. Replace it all and fuggedaboutit. Those parts aren't all that expensive either. The whole works should be well under $200US, possibly even under $100. You're gonna spend that much in wasted gas before you know it.

[wilkie3]

I'll check the filter. Who knows, anything can happen.

Can I get all of those parts from BMA?
What do you mean by crankcase ventilation and ICV plumbing?
How many different hose diameters are there?

[ScottyWM]

in my '93 525iT is about 22mpg city driving on premium (with EAT chip).

(Hey, just checked your profile - you're a QE!? Me too, well metrologist actually, but do a lot of QE stuff.)

1. What is a good way to locate my vacuum leaks?
2. So a hissing sound in the intake is not normal?
3. What mileage should I be getting, in general?

I performed a reboot, but no change.

Thanks.

[SRR2]

There's a hose from the valve cover from (usually) the air-oil separator that routes crancase gases back into the intake to be burned. That hose is one fo the first to get rock-hard, and a good candidate for air leakage. I don't know whether your engine has an ICV, but if it does, it's another good candidate for leakage. The ICV, if you have one, bypasses filtered intake air around the throttle plate to set the idle speed. ICVs are a common source of idle-related issues like wandering RPM, stalling, poor driveability at low speeds, etc. Cars that have stability management don't, to the best of my knowledge, have them since they have electronically controlled throttle plates which are also used to control idle speed, thus there's no reason to add an extra control for the same purpose.

Also, make sure your dipstick seals correctly in the tube and the oil-fill cap is tightly sealed to the valve cover. Air leakage past the dipstick or fill cap into the crankcase will upset the applecart for sure.