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Discussion Starter · #1 ·
My Celica has been running little rough lately been throwing parts at it to no avail. I've taken a video but will list what I've done to it first. The father is a mechanic so we've hooked a OBD1 Scanner to it to see if it had thrown any codes which it hasn't he did notice the O2 Sensor was stuck on lean which we replaced that but still shows stuck on lean. We've replace spark plugs, fuel filter, O2 sensor, checked plug wires with meter, taken IAC off checked to make sure it was opening and closing and also checked ohms... it checks out fine, did a compression check on all cylinders they are all fine. It seems to only do this at idle and under 3k RPM once passed that is seems to clear up. Any help would be appriciated! Video to what it sounds like below. (The plug wires bouncing around is when its running like crap)

 

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Lean is usually a vacuum leak, or dirty throttle body.

Check those, and also verify that the O2 sensor is bouncing (showing the computer is adjusting fuel)

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Discussion Starter · #3 · (Edited)
Lean is usually a vacuum leak, or dirty throttle body.

Check those, and also verify that the O2 sensor is bouncing (showing the computer is adjusting fuel)

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Throttle body was cleaned when we had the IAC out and off. Will check hoses more. Also how would I verify that the O2 sensor is bouncing when the scanner doesnt show anything but it stuck lean?
 

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Discussion Starter · #5 ·
How is the time? Also check the dostributor for oil internally
Timing is fine and cap has been off and inspected. Think we have narrowed it down to MAP sensor. Every time we pull the hose off it will run crappy obviously but once plugged in wont do the rough idle for sometime then eventually start back up. Im wondering if i can put any used MAP sensor from Ebay from a 5SFE motor or do the serial numbers on the MAP sensor have to match? Brand new ones are crazy expensive.
 

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Normally, when the vacuum hose is unplugged from the MAP, the engine will die. If yours still runs then
  • ecu might be in open loop, and ignoring the map sensor. This could be due to the eco thinks the engine is cold, or is not receiving valid information from the sensors it needs to control AFM.
  • the map sensor and o2 sensor are feeding extreme data such that the map sensor was suggesting very low vacuum (little fuel needed) and the o2 sensor instructed the ecu to add more fuel to compensate for a very lean condition.

The FSM has instructions on how to test the map sensor using a manual vacuum tool and a meter to check resistance.

(It's always good to diagnose before throwing parts at the car. You'll learn more by doing add diagnostics)

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Discussion Starter · #7 ·
Normally, when the vacuum hose is unplugged from the MAP, the engine will die. If yours still runs then
  • ecu might be in open loop, and ignoring the map sensor. This could be due to the eco thinks the engine is cold, or is not receiving valid information from the sensors it needs to control AFM.
  • the map sensor and o2 sensor are feeding extreme data such that the map sensor was suggesting very low vacuum (little fuel needed) and the o2 sensor instructed the ecu to add more fuel to compensate for a very lean condition.

The FSM has instructions on how to test the map sensor using a manual vacuum tool and a meter to check resistance.

(It's always good to diagnose before throwing parts at the car. You'll learn more by doing add diagnostics)

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Oh it will die once the hose is unplugged from the MAP sensor, but usually after pulling it off and killing it once plugged back in and started it will run fine with no hiccups for good 10 min and slowly start again. Usually it starts the hiccups bout 30 sec after its started cold and driving.
 

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Sounds like it is going into open loop after map disconnect. On restart, 30 sec for the ecu to verify temperature and sensor signals. One of the sensors is out of wack or the wiring is reducing voltage on the return signal.

You'll need to check the sensors (using the FSM) at the sensor and again back at the ecu.


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Timing is fine and cap has been off and inspected. Think we have narrowed it down to MAP sensor. Every time we pull the hose off it will run crappy obviously but once plugged in wont do the rough idle for sometime then eventually start back up. Im wondering if i can put any used MAP sensor from Ebay from a 5SFE motor or do the serial numbers on the MAP sensor have to match? Brand new ones are crazy expensive.
Get that thing running right yet?

Just a quick note about MAP sensor: it can be bench tested with a few basic tools, if you want to know for sure if it's good or not (will require a voltmeter, vac gauge, some hose, and a steady 5v DC supply from phone charger or similar). Secondly, MAP sensor from an early 90s 5SFE Camry has slightly different form factor but same specs and will work; I'm running one on my car currently because they're easy to find and cheap.
 

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Discussion Starter · #10 ·
Get that thing running right yet?

Just a quick note about MAP sensor: it can be bench tested with a few basic tools, if you want to know for sure if it's good or not (will require a voltmeter, vac gauge, some hose, and a steady 5v DC supply from phone charger or similar). Secondly, MAP sensor from an early 90s 5SFE Camry has slightly different form factor but same specs and will work; I'm running one on my car currently because they're easy to find and cheap.
Yes actually yesterday after waiting a few weeks at a shop that never got time to really mess with it. One guy was checking for spark said the valve cover was leaking and also one of the plugs had filled with oil said that probably wouldnt be it so i decided to buy new gasket and brought it home to work on it myself. well when we took the valve cover off to replace the gasket we decided to pull the PVC valve and by god the thing was all gummed up and stuck open or closed but was making one hell of a vacuum problem. Cleaned it out put it in and runs like a whole new car. Bought new valve and installed today. Thanks all for trying to help...was a simple 5 dollar part :(
 
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