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2000 Corolla Ve Rough Start When Warm P0171

By The Flush October 28, 2011



I have a 2000 Corolla VE 5 speed manual with 146,000 miles that I have trouble starting only when the engine is warm and it has CEL P0171.

I bought it used in 2006 with 89K miles. Original owner said he used synthetic oil with extended change intervals and he swore it did not use any oil. I did not check it thoroughly before buying, but found out quickly that it was using oil at a rate of a half quart per tank of gas. It also had whichever CEL that referenced a bad MAF sensor. Cleaning the MAF did not help, but the car drove fine with the CEL and I averaged 38 MPG for 5 years while adding oil at every fuel up. Somewhere in there I changed the PCV because I was told it might help with the oil usage, but it did not. The CEL would come and go (I never bothered to check what codes were showing). This Spring it started driving rough and hesitating unless I gave it a lot of gas. After a particularly rough ride home from work, I thought it was dead because when I checked the oil, there was none showing on the dipstick. I did get it run long enough to get it to Autozone to check the codes, which were P0300 (multiple misfire) P0303, P0304 (misfire cylinders 3 and 4), and P0171 fuel injection system lean. When I checked the spark plugs, they were completely worn out. After changing plugs, the engine fired right up and I thought it was fixed. No more CEL. Air filter was dirty, so I vacuumed it, although I have not replaced it yet. However, when I drove it long enough to get it warm, it would be difficult to start back up. Kind of a coughing start and then a lot of shaking until it got going, then it would be drivable, although maybe not as smooth as I would like. I have added a bottle of Gumout Regane, but have not driven a full tank with it yet. In the mornings when the engine is cold, it has no problems starting. After a week, CEL came back on which I just got checked and found to be P0171 again. Autozone suggested it could be a bad camshaft position sensor or bad O2 sensor. I do not want to just start replacing parts without some diagnostics first, so I did not buy either part. Haynes manual says to check resistance of the cam sensor, which seems to be fine (1250 ohms). Have not had time to check anything else.

What do I need to be checking (and how) and in what order?

P0171 could mean the MAF is dirty again, or it is bad and needs replaced, or a vacuum leak. Not sure what you used last time when cleaning the MAF, or what procedure you used, but I would only use CRC QD electronic cleaner and make sure to remove it.

 

Remove the MAF sensor that is located on a big hose that connects air filter box and engine. Clean it with CRC cleaner couple of times at 5-10 minutes interval and then reinstall it. Then put in a new air filter immediately after cleaning MAF sensor so if dirt is the problem, it doesn't get dirty again. Then either clear the code using a scanner, or unbolt and reconnect the negative connection on the battery to reset the computer and go for a drive. If it doesn't help, try and replace it with a known-working-good one from a friend's car if possible before buying one to rule out it is the MAF that is the problem.

If the MAF is not the problem,

  • Inspect all vacuum and PCV hoses, replace if necessary. (listen with a peace of tube up to your hear, and spray carb cleaner and see if idle changes)
  • Check for a dirty fuel filter and proper fuel pressure (go to autozone and borrow a testing set for free and perform the following)
    Fuel pressure:
    301 - 347 kPa (3.1 - 3.5 kgf/sq.cm, 44 - 50 psi)
     
    If pressure is high, replace the fuel pressure regulator. If pressure is low, check these parts:
  • Fuel hoses and connections
  • Fuel pump
  • Fuel filter
  • Fuel pressure regulator

(l) Start the engine. (m) Measure the fuel pressure at idle. Fuel pressure:

301 - 347 kPa (3.1 - 3.5 kgf/sq.cm, 44 - 50 psi)

 

Stop the engine. (o) Check that the fuel pressure remains as specified for 5 minutes after the engine has stopped. Fuel pressure:

147 kPa (1.5 kgf/sq.cm, 21 psi) or more

 

If pressure is not as specified, check the fuel pump, pressure regulator and/or injectors.

(p) After checking fuel pressure, disconnect the negative (-) terminal cable from the battery and carefully, remove the SST and fuel tube connector to prevent gasoline from splashing.

SST 09268-41040, 09268-41250, 09268-45012

 

What the Autozone idiots told you already about it being a bad camshaft sensor is highly unlikely, and O2 sensor is possible, but probably not the issue. Could also be a leak around the intake manifold gasket which you can spray some carb cleaner by to rule out if no change in idle occurs.

Troubleshoot all these areas listed and this should help.



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