Starts and idles well. Works normal with light throttle but bogs with moderate to heavy throttle. Any ideas ?

740 or 760? Normally aspired or Turbo? I-4 or V-6?

How many miles? Any mods? Auto or Manual Transmission?

Would you know what version or type fuel injection?

Do you keep up with maintenance? (As with Amarin's clogged air filter reply, I imagine. We can only guess and need a little more info.)

How long have you owned it? How long has your 1986 700-series been exhibiting such behavior?

Any recent repairs with the electrical, ignition, or fuel control system? Please?

Presuming you keep up with rotor, wires, cap, air filter, and know the foibles, so in good or maintained condition, a bogging may be a faulty throttle position switch. Presuming an I-4 redblock engine with some form of the LH-Jetronic fuel control / EZK ignition. (I'm unsure the model year range Bendix Rex ignition / Regina fuel control was part of the non-turbo 700-900s with the square ignition coil.)

Yet can be intermittent faults with ignition, fuel, all connected items along the engine control wire harness, power to the engine control system including connection to ground, faulty emissions controls (emission controls must work well for good performance and fuel economy), faulty fuel delivery including fuel rail pressure regulator (two different types depending on fuel injection type). Post air filter air intake vacuum leak (maybe not).

Indicate what nation or state or location? Got rust or rust free?

Any dash lights to CHECK ENGINE or well, I dunno.

Please lettuce know. Volvo scholars much greater and more powerful than I will provide guidance.

Välkommen to the mighty and powerful brickboard!

cheers and thank you and Happy Holidays!

Grumpy Boyeeeeeee.

Its a one owner car with 985000km. It has had all necessary maintenance. It is a turbo car. Air filter is clean. Belt timing and ignition timing was checked. We suspect the air flow sensor but don't how to check it. New throttle switch was installed which helped slightly.

When my AMM went bad. I could rev in neutral. But in gear, bogged down, coughed, sputtered. Check your air intake hoses. They get soft and collapse when accelerating.
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Post Back. That's whats makes this forum work.

985000 kms? 612000 miles!

I'll imagine you are in a commonwealth nation, then?

So, no dash light such as the CHECK ENGINE?

Yeah, the simple stuff like aleekat with collapsing turbo hoses (and leakage or vacuum / boost at the air filter box from the (amarin asking of a clean) air filter rearwards.

I'll guess you have an intercooler? I've read, yet not encountered, a failed intercooler that some how lost seal. It had fractured along a molding seam or where the rubber turbo output pipe secured to it? I forget. I read it on a turbobricks thread or maybe here on the brickboard a long time ago.

I'd inspect the air induction intake system for seal loss due to connections needing a good re-seat or replace failed components like the soft turbo air hoses.

You have, than, LH-Jetronic 2.2 and EZK115 or EZK117 (I forget what one is used with the Turbo) with hall effect for engine timing in the distributor.

You also have, then, the Bosch AMM ON 0 280 212 007 (0280212007). Have you swapped in a known good AMM / MAF.

Please see:
How can I tell which version of Bosch LH Fuel Injection is on my Volvo 240?

https://www.ipdusa.com/techtips/10087/how-can-i-tell-which-version-of-bosch-lh-fuel-injection-is-on-my-volvo-240

In concert with an air induction system check, you could swap in a known good working AMM / MAF.

Else, with ignition OFF and key out of the ignition, you can try disconnecting the wire harness connector from the AMM (ensure the silicon seal does not fall out of the connector!), start the engine and see how it behaves. With the MAF sensor disconnected, the LH-Jet defaults to a "limp home" mode that runs the fuel mix really rich.

Indeed, you can test the AMM using the limited OBD function in your 1986 Volvo 740 engine control systems (2 - LH-Jet 2.2 and the EZK ignition)

Please see:
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm#Bosch22Codes

Though the OBD deals with thresholds and the control system is very tolerant (forgiving) of a fault condition before setting a fault code and a on-dash CHECK ENGINE light.

Using a known good multimeter with continuity check, and resistance (OHMs), you can test the connected AMM. Also, you can test the oxygen sensor. These two components are used by the engine control systems to verify a balance of air and fuel the engine consumes and the amount of oxygen in the exhaust.

Though to describe the method of testing the AMM would take me a small novel. Others like Art B. can better explain to you. You can also search this forum using the search feature, as well as other forums, You Tube, and what fave search engine works best for you. Same goes for the testing the oxygen sensor as the procedure is detailed here on this forum many times over.

Inside the air filter box is the preheat diverter flap valve. I'm sort of certain on the 740s with LH-Jet 2.2 it fails to allows preheated air only, as it does on 240s. In the hot summer time, the AMM / MAF can fail quickly.

You can replace the springy thermostat with new. They seem to not last as long as what the factory put in. Maybe a new one every air filter? Some will use a nail and force cold air all the time - may be okay in warmer climes.

Volvo 740 Air Box Thermostat



Wahler OEM PN 70411
Volvo PN 1266826

https://www.fcpeuro.com/products/volvo-engine-air-box-thermostat-1266826

There would be more items to check such as pressure at the fuel rail, electrics in good condition. The relay / fuse platform at the center dash, behind the ash tray is a serviceable item as corrosion forms at the wire harness spade terminals, with barb, that secure under the platform, and the relay 'prongs' make contact when you seat them. At nearly a million kms, it would not hurt to pull away the center console dressing (carefully) and inspect it, if not already. Where the fuel pump relay sits on that relay, sometimes on can find heat distorted plastic.

You replaced your throttle position sensor (TPS) and your 1986 Volvo 740 Turbo idles just fine?

Also, all connectors along the wire harness - these can form corrosion. Usually a white coating on connector pins at the ignition power stage, the fuel control and ignition control ECUs wire harness connector. Ity can help to treat these connection with DeoxIT, a dielectric low-voltage (usually DC power) anti-corrosion product. Treat connectors with such.

Clean the throttle body?

Check the fuel rail pressure regulator (FPR)? The vacuum line between it and the air intake port. If fuel drips out, replace it.

As for fuel rail pressure check ... I'm unsure how to do so save for at the FPR to fuel rail out connection with a dial gauge meant for it. You could start for a listen to the intank and the main fuel pumps. If bogging is more an issue with a low fuel level in the fuel tank, the intake pump may be at fault, or a submerged hose connection between the in-tank pump out to the top of the tank fuel sender assembly may be rotten. At nearly 1 million kms, many of these components would need to have been replaced at least 2-4 times or so.

If you can listen to the main fuel pump run, does it make much noise? A quiet, smooth hum with a little buss, or like a heavy glass jar fuel of bees that with some skips or inconsistency in the sound? The main fuel pump may not be well primed, is old, or / and may have some resistance from the downstream fuel filter. Though, unless rust in the tank or other particulates, I'd not encountered an old fuel filter that was so clogged as to prevent fuel delivery.

Search this forum for testing fuel rail pressure for LH-2.2 equipped autos. Check what records you have of wear items replacement.

As the OBD on your model year is very limited, it may help to use the multimeter to test connected engine control components, continuity and resistance checks of connected sensors and devices.

So:
1. Vacuum leaks, air filter, air filter box preheater
2. Disconnect AMM. Run the engine. Different behavior?
3. OBD check with LED test light. May need to fabricate test light
3. Swap in known good AMM? Different behavior.

After that, the issue may require a more serious diagnostic and repair.

Though others will have more concise as I tend to go on so.

Questions?

Hope that helps.

Power Systems and Thermal Control SCADA Systems MacDuff.