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Old 11-22-2021, 06:32 PM   #1
noz-e8tr
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Default 93 940 N/A (Rex/Regina) Very Rich at Idle

Help me....I'm running out of ideas.
This is a N/A Rex/Regina, so we are looing at an air intake temp sensor and MAP sensor. No MAF Sensor. At idle its sickly rich. If I idle for 5+ minutes it starts to load up like a carbed car dumping fuel. It starts to stumble and I have to put it in neutral and rev to clear it out. The gas smell from the exhaust has every one hating me. Here is what has been done.

New O2 Sensor
New MAP Sensor
New Intake Air Temp sensor
New ECU Temp sensor
New Injectors (reconditioned)
New Fuel Pressure Regulator
I've verified correct vacuum at idle to make sure exhaust is not clogged (will mess up a map sensor reading)
I adjusted Throttle Position sensor (but have not replaced it)

My MPG is 20-22 in town, so it seems to predominantly be at idle. Idle does bounce around slightly as if a small vac leak is present, but I have yet to find it (could also be a result of inconsistent fuel). Usually a vac leak in the MAP will cause them to run lean unless the leak is on the MAP circuit...it is not. I'm throwing no check engine codes either.

Not sure if this one has a cold start injector. But that is what I'm checking next. Perhaps the injector is leaking a bit. Anyone got any other ideas? I'm really running out of them myself.
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Last edited by noz-e8tr; 11-22-2021 at 07:04 PM..
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Old 11-23-2021, 01:31 PM   #2
oldnfast
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Quote:
Originally Posted by noz-e8tr View Post
Help me....I'm running out of ideas.
This is a N/A Rex/Regina, so we are looing at an air intake temp sensor and MAP sensor. No MAF Sensor. At idle its sickly rich. If I idle for 5+ minutes it starts to load up like a carbed car dumping fuel. It starts to stumble and I have to put it in neutral and rev to clear it out. The gas smell from the exhaust has every one hating me. Here is what has been done.

New O2 Sensor
New MAP Sensor
New Intake Air Temp sensor
New ECU Temp sensor
New Injectors (reconditioned)
New Fuel Pressure Regulator
I've verified correct vacuum at idle to make sure exhaust is not clogged (will mess up a map sensor reading)
I adjusted Throttle Position sensor (but have not replaced it)

My MPG is 20-22 in town, so it seems to predominantly be at idle. Idle does bounce around slightly as if a small vac leak is present, but I have yet to find it (could also be a result of inconsistent fuel). Usually a vac leak in the MAP will cause them to run lean unless the leak is on the MAP circuit...it is not. I'm throwing no check engine codes either.

Not sure if this one has a cold start injector. But that is what I'm checking next. Perhaps the injector is leaking a bit. Anyone got any other ideas? I'm really running out of them myself.
I believe Volvo has a TSB to eliminate the cold start valve on the Regina. I just looked quick but couldn’t find it. Maybe on brickboard, I’ll keep looking
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Old 11-23-2021, 01:59 PM   #3
dl242gt
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I would double check that the O2 sensor is the correct Rex/Regina type. Also measure the coolant temp sensor at cold, warm, and hot temps to make sure it's working properly. I once encountered a coolant temp sensor that went open circuit when the engine warmed up caused super rich running. Didn't set any codes.
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Old 11-23-2021, 07:36 PM   #4
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Weak link is usually the fuel pump. Only one on those and it is in the tank...
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Old 11-23-2021, 08:42 PM   #5
lookforjoe
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If none of the new parts made any difference, were they all OEM supplier parts?

Doesn't seem likely the fuel pump would cause a rich at idle symptom, though.

Leaking CS valve could load it up at idle.
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Old 11-23-2021, 08:43 PM   #6
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Have you checked the plug wires and plugs? Do the plugs look equally awful?

You can still find the TP31903/1 Regina greenbook (partial copy) via the Internet Wayback Machine (e.g. link)

Some of the sensor measurements, especially if measured from the Regina connector, would help rule out bad sensors/wiring.
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