THE CAR: 1989 744 GL with Bosch LH 2.4 and 230k miles, auto.

THE PROBLEM: Intermittently, it will just bog, engine will not rev, very slight hint of backfire/misfire while accelerating from a dead stop. It also cracks, once in a while, like it is backfiring through the intake. To test it, I sometimes do a brake stand to see what it will rev to under the load - its an NA so it never spins the tires - but if its "acting up" it will do like 1400 RPM and miss, if its being normal, it will rev to 2000 RPM and grunt.

Its almost like something will click (no clicking noise, however) and it will accelerate with full power after the bogging, which can last for 4-15 seconds under normal acceleration.

It also acts up occasionally while accelerating slowly (not causing a downshift), at other speeds like 50 or 60 mph.

It will idle okay after the ECU is reset (I have just fixed some vacuum leaks). I can't say how it will idle once it re-learns in the absence of vacuum leaks. I am also curious to see if it will learn around the hesistation.

WHAT I'VE DONE:
With the low air-flow conditions it really seems like it would be the AMM, but I have swapped another in and no change. I have removed the knock sensor from the block and tried to accelerate (while keeping the RPM under 3000 to prevent the check engine light). Again, vacuum leaks taken care of - new intake gasket, TB gasket, fuel injector o-rings and cleaned TB. I want to drive around with a fuel pressure gauge hooked up to make sure the fuel pressure regulator isn't lazy or the fuel pump for that matter. In the diagnostic mode in OBD-I, LH sees the throttle open via the TPS, and it also clicks. New 02 sensor, AMM was cleaned a couple months ago.

Any ideas?

I want to recheck and see if this condition happens with the AMM disconnected and maybe the wiring to the AMM.

Thanks,
Smith

I agree with Jas645 - IAC valve. Before cleaning it though, make sure that the Throttle Position Switch is clicking as you take the throttle off and on the endstop. This is what switches IAC operation in and out.

When my IAC needed cleaning, the car would stall when I kicked down from a stop, or would hesitate badly when kicking down if coasting on the highway. Both symptoms cured by the IAC cleaning.



--
David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto

Idle Air Control valve perhaps?

My 1993 945 (a Rex/Regina car) had very similar symptoms. I removed and cleaned the IAC valve and tested its function per the FAQs and the problem was resovled.
--
1993 945 NA

Check the coil. I had the exact same symptoms for nearly 3 months. I did a complete tune up and replaced the FPR. Then I found one day that the coil was really hot. I replaced it and all was well again.

Some have reported poor running problems when the tank gets low due to in-tank fuel hose cracks. Does the poor running coincide with a low fuel level? You may have a bad pre-pump or clogged in-tank filter. Has the main gas filter been replaced recently? Check the distributor also for oil leaks that may have it gummed up inside.

Had the same problem with my '92 245-- I chased my tail for days swapping parts. I finally measured the output of the 6 month old Bosch replacement O2 sensor and was surprised to discover that its peak output was around 1.3V instead of 0.9V or so. Swapping in another sensor fixed the hesitation problem and an intermittent poor idle.

I didn't look at the sensor right away because I had replaced it so recently...

Good luck!

Herb Goltz, Aurora, Ontario, Canada

Herb,

I should've listened to your advice earlier but I'm a little too hardheaded sometimes. But guess how many volts my 02 sensor was putting out? 1.3!!!!!!!!! Bosch replacement for a Mustang that I soldered in.

Plugs were white. I went around and around today with this one... Replaced fuel filter, removed intake, cleaned IAC valve, checked wiring, replaced vacuum hoses, removed exhaust to make sure it wasn't a clogged converter, check fuel injector spray patterns, check fuel pressure, everything!!!

The thing is, this is the second bad 02 sensor I have had in a row, and yes, there is voltage going to the heater element. The first one was a universal NTK that lost the heater element (infinite resistance) and never stayed heated up at idle. Now this Bosch one that puts out 1.3 volts.. I tell ya, this one about made me push the car off the cliff when it wasn't a Volvo problem at all!!

Thanks again!
Smith

Hello Smith:

Thanks for the feedback! Diagnosing that problem was really tough-- I swapped piles of parts and and thought I was double and triple checking everything. When I finally took measurements on the O2 sensor, my first suspicion was that my multimeter wasn't accurate-- I couldn't get my head around the signal being so far out of range...

Some of the pros here have been complaining of declining Bosch quality-- Bosch stuff used to be above reproach, but apparently no longer...

I think the information about 1-1-3 and stray O2 sensor heater voltage belongs in the FAQ-- enough of us have encountered it, and not diagnosing it properly results in an expensive cascade of unnecessary parts-- thank God for pick-and-pulls!

I see you're from Plymouth-- my mother is from Sheboygan, and if memory serves, she and my father lived briefly in Plymouth 40 years ago!

Cheers!

Herb Goltz, Aurora, Ontario, Canada '92 245 140K mi, '92 945T, 206K mi

Hi Herb,

Yup after resetting the battery it threw the 1-1-3 code in minutes! I can't imagine how rich LH thought the engine was running! I agree about a little paragraph in the FAQs.

Sheboygan, I'm there all the time! That's interesting.... its a neat little area!

Take Care,
Smith

Fuel filter? Fuel pressure borderline? (from FPR or fuel pump)