91 240 Stumbling - IAC and TPS code

Help, what am I missing? 1991 240 NA. Car idles fine, but at 1500rpm it stumbles/surges and won’t make it past 2000rpm. Getting an IAC (223) and TPS (234) code. What I’ve done:
- cleaned IAC
- replaced TPS
- cleaned throttle body
- cleaned maf
- clamp IAC and dies from idle or if rev up contiunes to stumble/surge. Seems like IAC working fine.
- unplug maf and the idle changes. Seems like maf is fine and no leaks.
- checked exhaust isn’t plugged
- no obvious vacuum leaks
- unplugged and replugged ECM

It seems like TPS to me… believe I have it set right to click when throttle begins to move. Checked voltage and it seems on/off. I read 1991 is on/off is that correct? If so what tells the computer to add gas then?
Car was running fine, parked it in a garage for a couple months and now it’s doing this.

Any recommendations before I pull harness or look at swapping ECM?

****tt grounds at the intake?

ZVOLV said:

****tt grounds at the intake?

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The grounds on the intake and fuel rail bracket?
Checked them, looked fine, cleaned and still have issue.


I replaced the maf, still same issue.

Bricky McBrickface said:

what am I missing?

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Lower fuel pressure....filter/pump...check pressure

TPS has two positions...idle...peddle to the metal...not related to your issue.

Coil could be ohm spec'ed, but I don't think that's the issue.

When a vehicle sits, sometimes, an injector(s) can plug up....but I'd check rail pressure first.

How does it run with the maf sensor disconnected? Try disconnecting it and then starting and running the car. I'd also suggest a good look at the engine speed sensor. They can get weirdly intermittent and cause a poor signal to the EZK. Make sure the harmonic balancer isn't slipping. I second the suggestion for the fuel pressure check. I've had the internals fail in the the fuel regulator without the classic gas leaking problem. The fuel pressure became too high and was flooding the engine. You can check your plugs and see if it's been getting flooded.

84B23F said:

Lower fuel pressure....filter/pump...check pressure

TPS has two positions...idle...peddle to the metal...not related to your issue.

Coil could be ohm spec'ed, but I don't think that's the issue.

When a vehicle sits, sometimes, an injector(s) can plug up....but I'd check rail pressure first.

Click to expand...

Just replaced fuel regulator. No difference. Idles fine, surges at 2000rpm.

Fuel injectors are fine, unplugged each one and there was noticeable difference. I replace fuel filter when I got the car a year or two ago. Got another one just to confirm.

How do I check fuel pressure on these cars? I have the gauge kit, but there’s no good way to connect. Anyone have a specific part list to connect a guage?

Bricky McBrickface said:

How do I check fuel pressure on these cars?...surges at 2000rpm

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Quick & Dirty -

1. Disconnect return hose to fuel tank at FPR...hook a several foot hose to FPR, and stick in in a bottle...activate fuel pump(s) and see if fuel comes out in bottle. This would be done outside in open air...not in a garage.

2. Pinch down return hose at idle and 2000 RPM

84B23F said:

Quick & Dirty -

1. Disconnect return hose to fuel tank at FPR...hook a several foot hose to FPR, and stick in in a bottle...activate fuel pump(s) and see if fuel comes out in bottle. This would be done outside in open air...not in a garage.

2. Pinch down return hose at idle and 2000 RPM

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Don?t think i want to do that? rather hook a pressure gauge on and confirm there?s not a fuel issue. Anyone have a fittings list to hook up a gauge? Wish Volvo had a fitting like my Fords.

Last night check that both pumps are running so that should be okay.

I think the 93 and later 240/940's had a schaeder valve on the fuel rail. Maybe see if you can find of those?

Bricky McBrickface said:

How do I check fuel pressure on these cars? I have the gauge kit, but there?s no good way to connect. Anyone have a specific part list to connect a guage?

Click to expand...

Volvo has special adapters that tap off the fuel rail to connect to their gauge. I have the gauge and adapters available to rent.

http://hiperformanceautoservice.com/images/LHFuelPressureGaugeAdapter.jpg


Here's an adapter that will allow you to use your own gauge.

https://mrotools.com/71305-lang-volvo-adapter-14mm-lh-jetronic.aspx

Bricky McBrickface said:

Don?t think i want to do that?.

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Another Quick & Dirty

Remove FPR...with a shop air compressor, set line pressure to say 35psi...with hand "blow" tool with a rubber tip, pressurize FPR on inlet side...then up shop air to 40psi, then 45psi.

Air should come out at 45psi or there abouts.

So, if FPR passes, reinstall with new o-right, and then do my return to fuel tank test, with a bottle.

Oh, been here, done that...but I do have a shop compressor setup so I can regulate pressure on service line.

Thank you hiperfauto, I’ll see if I can track down fittings.

Both pumps are working. In process of replacing filter even though I did it a year or two ago. The line between pump and filter broke so waiting on part,

Don’t think it’s a timing issue, but going to confirm. Then checking ecu connection and possibly look for replacement ecu.

Bricky McBrickface said:

Don?t think it?s a timing issue...

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CPS (crank position sensor) can have an erratic behavior before finally failing. If issue will act up while parked, I'd use a timing light, and increase engine RPM.

Is this issue load based (under a load...driving around)?

Haven’t been able to drive it.

SOrry to hijack, but I also am in need of checking fuel pressure on my 91. How does that adapter work? I'm failing to see how it connects. I assume it threads to the supply line from the tank and then the hose but that compression fitting confuses me

I forget, can the IAC plug be crossed with the TPS plug?

I would peel back the boot on each connector and inspect the terminal crimps for corrosion. You also wanna check each wire on the circuit (end to end) for excessive resistance.

Drag test each female terminal with a male terminals donated from a spare component.

I have never seen a TPS switch fail on these cars, but it is possible.

Make sure the TPS is adjusted correctly.

ZVOLV said:

TPS

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Two Functions:

1. Idle Air Control - Once off idle, driver's foot controls air going into intake

2. Peddle to the metal - More fuel (maybe timing change also)

Unplug the TPS and the ECT connectors. Unplug the ECU/EZK boxes and remove the sheaths. BACKPROBE the connectors and confirm less than about 2 ohms tip to tip. I like to see 0.3 ohms on the ol Fluke meter.

I have seen bunk/misleading codes by LH.

I'm thinking this isn't electrical, its fuel pressure barring some animal made a nest in the airbox. If you hadn't already replaced the regulator, that's what I'd think.

I like to know the pressure is right too. The fittings are now available to buy, a bit easier than when I made my adapter 20 years ago, however the quick and dirty test I use is a tad different from what was already suggested. A lot quicker and a lot less dirty. And safer if you do it without trying to run the engine at the same time. Run the pumps without running the motor by getting power from fuse 6 and putting it to fuse 4.



It is easy to feel the pressure in the return hose. I suspect you won't feel any. Before you blame the main pump remember it needs both power and fuel on the suction side from the tank pump, so it could still be an electrical problem. And don't discount the possibility the new regulator is no good -- they're not being built en masse any more.



Pulling the vacuum hose just allows you to confirm the diaphragm isn't ruptured sending fuel to the manifold by shortcut.



My adapter was made from pieces of a junkyard fuel rail. The Volvo tool would be easier, but you can't get it at Autozone.

Finally got a fuel pressure gauge on. For anyone interested M14x1.5 kind of seems like the right thread, I do NOT recommend leaving that on for long term. Short term testing it seemed to seal okay. Ended up using a brake fitting block and using tap and die set to make things work.

Anyways, ~35psi pressure. Pressure was consistent at idle, increased rpm and when surging. When the regulator vacuum was disconnected the pressure increased to around 45psi.I’m not sure what pressure is supposed to be, but no pressure drop indicates to me that it’s not running out of gas.

Checked timing - indicator is difficult to get a good reading. However timing is decreasing with rpm. With fast throttle the timing sharply decreases. Going to check crank position sensor for crud or damage before trying to replace it.

After that I’m out of ideas. See if I can find another ECU I guess?