(FIXED)1994 Toyota Camry Rapid fuel consumption

Was given a 1994 4 cylinder Toyota Camry. Has 240 K on the odometer but the motor and tranny was recently swiped out. On my way back the car ran through $20 worth of gas in under an hour. When I parked the car noticed, black smoke from the exhaust. So that tells me there is a rich condition going on. During the ride i could smell eggy fuel fumes coming from the exhaust at times. Wasnt a rotten egg smell that people referred to as a bad catalyst but it was a poor fuel smell. There are no noticeable fuel leaks.

This being my first Toyota there are a few sensors and things under the hood that are quite new to me that I'm still learning about. I can't also seem to test fuel pressure because I don't have the banjo fitting for my gauge.

I would assume the fuel pressure regulator was an issue but something that caught my attention was a vacuumline disconnected from the map sensor and plugged with a screw that runs from a vacuum switching valve which also has a line leading to the fuel pressure regulator. I can't find much info on this switching valve other than it's used 4 fuel control but i can put my finger on the valve and feel suction.

I ran a new vacuum line from the valve back to the map sensor and when plugged in the engine idles at 2000 RPM at a constant. I'm sure this is why the vacuum line was disconnected and plugged. I have no way to test whether my map sensor is faulty right now as I have no access to a vacuum pump and No T pins to back probe connection when in use To see if the sensor responds to vacuum changes with my multimeter.

The fuel pressure regulator could be shot but now I'm questioning whether the map sensor is at fault as I know in some cases a faulty map sensor will show signs similar to that of a failed regulator as the computer no longer has input from that sensor. The sensors electrical connector was left plugged in so I assume the engine computer would have been getting an atmospheric pressure reading under all engine loads.


Will have to get a new fuelpressure testing kit as well as a vacuum pump once I get paid but just posting this to see if anyone has any ideas as to what could be the cause of the slight hesitation and jerking on acceleration and poor fuel economy.


Attached is an image of the vacuum distribution for the vehicle for further clarification.

I'd suggest the map was unplugged to mask the high idle. That'll definitely make it drink fuel. The only thing I'm not familiar with is the switching port you mention.

Trying to keep things basic, what if you plug the map back in and run the engine. After about a minute you should see the oxygen sensor start switching rich/lean and this will confirm your economy and fuel smell problems are probably sorted. Then you may just a high idle problem.


Sent from my iPhone using Tapatalk

matt.white wrote: I'd suggest the map was unplugged to mask the high idle. That'll definitely make it drink fuel. The only thing I'm not familiar with is the switching port you mention.

Trying to keep things basic, what if you plug the map back in and run the engine. After about a minute you should see the oxygen sensor start switching rich/lean and this will confirm your economy and fuel smell problems are probably sorted. Then you may just a high idle problem.


Sent from my iPhone using Tapatalk

Is it possible the map sensor could be faulty causing a vacuum leak when the vacuum line is plugged in? Im going to test the map sensor tomorrow once i get a chance.

Re: switching valve.. there seems to be 3 of these valves on this engine one for the AC another for fuel regulation and another for EGR control. The one I'm referring to connects to the fuel regulator vacuum switching valve with two lines. one runs to the fuel pressure regulator and the other runs to the map sensor


I've attached the layout of the vacuum distribution for further clarification

It could be leaking but should be simple to check. I'd still suggest it'd be better plugged in and leaking than not attached at all.

The pressure regulator and MAP plug into that two outlet fitting that may have a filter or something in it but as long as vacuum passes through it I wouldn't stress about that.

The idle-up valve is simply a solenoid to allow air to bypass the throttle and increasing the idle. That may even be a problem. If you disconnect that and plug the fitting in the manifold see if it idles lower.

Can you put a multimeter on the o2 sensor wire and watch it work with the MAP plugged back in?


Sent from my iPhone using Tapatalk

Had the idle up valve confused with the gas filter.

If I connect the mapsensor as usual the O2 sensor oscillates as it should. if I unplug either the electrical connector from the map sensor or the vacuumline it will stick rich @ .95.. or .96... is there any relationship between the mapsensor and the O2 sensor?

That would pretty much explain the blacksmoke I'm assuming as the vacuumline was plugged when I first got the vehicle.

I'm going to test for a vacuum leak once I get the chance

Did you try plugging the line to the idle up valve as Matt suggested?

Sent from my SM-N920P using Tapatalk

I tried plugging the only one i could locate which was the egr idle valve. It made no difference.

Also.. I put my vacuum gauge on the engine and its reading 15 inches of mercury. Seems a little low in my experience. When I rev the engine with the map sensor disconnected vacuum increases in the engine to 21 inches.. With the map sensor connected no need to rev the engine as something is causing it to rev anyway and I'm getting the same results. Isn't vacuum supposed to decrease as throttle opens? Is this normal if not what's the explanation for that?

I'll try to locate the other idle valve once I can get to it again. Trying to form a plan

Total relationship between MAP and o2 sensor. Map is manifold pressure. A reading of atmospheric pressure tells the ecu there is no restriction from the throttle so indicates full throttle. That tells the ecu to give the engine loads of fuel. That creates a rich condition. If it cycles rich lean with it plugged in I'd suggest you're well on the way to having your problems fixed.

You need to find where the engine is getting its excess air from. Does the throttle stop screw look like it's been played with? Can you post a photo of the throttle body? The idle up valve should be located on the firewall fairly high up behind the intake manifold if my memory serves. I think there's also a idle bypass adjustment. The other thing to check is the coolant hoses to the throttle body are getting hot and have good coolant flow.


Sent from my iPhone using Tapatalk

Ok. So that explains the rapid fuel consumption if the 02 reads rich ALL THE TIME with map disconnected at vacuum line. makes sense..

Something is definitely going on on the intake side. Wont be able to get back to it til wed. I want you to help me understand something... what exactly causes the high idle to stop if there is a an ivle misadjustment or vacuum leak with the map either disconnected electrically or via vacuum line (given the port the line runs to is sealed off) .. and what is going on with the map relationship to this supposed vacuum leak or extra air intake that causes the engine to idle higher when the vacuum line is reconnected to the map? Im just not understanding this. If there was a vacuum leak or idle adjustment wouldnt the problem still be present even if the map vacuum line was plugged? Or is the map telling the ecu to chill out when its reading atmospheric pressure?

Also what is the purpose of the vacuum throttle opener?

If youve already explained it then my apologies but just please clarify one more ttime. These things can get a bit confusing.

MAP disconnected was causing 02 to read rich at all times.. alluding to high fuel consumption.

plugged in to discover high idle speed issue..problem was throttle cable was adjusted too tight..

Good find

Sent from my SM-N920P using Tapatalk

Glad it's fixed


Sent from my iPhone using Tapatalk