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Discussion Starter #1 (Edited)
I found this forum last week, hoped it would provide some insight to the worsening problems of my 1999 RAV4. I was impressed by breadth and depth of knowledge in the community, and you're willingness to engage with first time posters. The summary below was written by my mechanic, who has done all* the work/service on my vehicle. *(except once, when i allowed a street mechanic to replace radiator)

It's a long read - from what i read here, 4.1 problems can stem from the most unlikely sources (this forum is like House, for cars) - describes current issue and work that preceded.

Thank you in advance for your help - suggestions, advice, and/or recommendations for an electrical specialist in Los Angeles area.

1999 Toyota Rav4
2.0 automatic transmission 4x4
208,000 miles


No aftermarket alarm system installed.

Current status
  1. Engine will not run well enough to drive. Never know when it will run without issues. Not driveable.
Past history (2 years 2 months with current owner)
  1. Intermittent check engine light pulsing and engine bucking. (within last year)
  2. Sometimes engine would stall and start up. This went on for months (infrequently, est. 10 or less times per month, no discernable pattern) - since Feb 2019
  3. Regular oil changes and maintenance. (throughout ownership)
Recent history (approx 3 week time frame for all below)
  1. Engine had noise for several weeks and had intermittent misfire with check engine lamp coming on then going out. This happening intermittently.
  2. Engine stalled and towed in to garage. Won't start.
  3. Car towed to another garage for repair. Diagnosis was no compression and coolant coming from front of engine.
  4. Engine had frozen water pump and oil spread out behind timing covers as well as firewall and suspension.
  5. Engine repaired
    • with cylinder head rebuilt
    • with valve guides and valve adjustment.
    • New seals on cam, oil pump shaft and crank shaft.
    • Vehicle was delivered with no issues.
  6. Next day owner reported temp gauge going hot at 50 mph.
  7. She brought it back to me. Went for test drive 5 miles without issue.
  8. Installed new thermostat and seal.
  9. Complaint check engine flashing and bucking.
  10. EGR was serviced, idle speed controller disassembled and cleaned, check for air leaks, scanned the engine and got no codes.
  11. In the meantime over 5 days on and off starting, driving cold engine and warmed engine the engine would run fine and without warning start flashing check engine lamp and bucking.
  12. On the 5th day with engine running at temperature and the temperature gauge was bouncing at "hot" and the scanner read 208 degrees F and the tach was bouncing all over the meter.
  13. Changed the ecm and still the same problem.
  14. Installed the original emc after 2 days of no improvement. Problem got worse after looking for possible wiring problem.
  15. Shook wiring near battery box with engine running and engine stumbled but kept running.
  16. Then problem got worse. Scanner connected and engine running observing live data and no codes.
  17. Temp gauge shows hot and engine will not accelerate past 3000 rpm without bucking. Disconnected scanner and engine died. Plugged in scanner and engine started. This happened three times.
  18. Shook same wiring and engine started. Temp gauge goes to "H" after warm up and tac bounces when check engine lamp is flashing. Scanner show no codes.
Current status
  1. Engine will not run well enough to drive. Never know when it will run without issues. Not driveable.
 

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-- Was an OEM thermostat installed? An OEM thermostat is critical, because it has a "jiggle valve" built into it that helps bleed air. People have reported problems with their Rav4.1s when they did not use an OEM thermostat (or at least a thermostat with the jiggle valve).

-- Consider replacing the ECT sensor, Toyota part number 89422-35010. This forum has had several reports recently of rough running that was corrected by replacing the ECT sensor. Its location is pictured below:


-- Keep checking for stored codes.
 

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Discussion Starter #4
Confirmed the thermostat has the jiggle valve. He's replacing the ECT sensor as suggested. I'll let you know what happens.
 

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An unintentional double post. Not sure how to remove it.
 

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Well; congratulations! You have almost found the problem.
Basic electrical troubleshooting, if you can move some wires and cause the problem to come and go, then you just need to figure out which wire or connector is the problem! But you are very close. I would start with the ground wire since it is a known trouble spot; although it is more of a system than a wire and you need to check each end, of each section, of the ground wire. But the wires you are moving may not include a ground wire.

A few notes of the diagnostic codes:
When you erase the codes the ECU also forgets what it has learned about the engine and it will need some driving time to relearn the settings the engine needs for top performance.
Most of the diagnostic codes are not instant. Some need to see errors on several trips and others need to see a certain driving pattern before they set. While you are out driving around for the ECU to do the diagnostics, it is a good time to watch the live data for any trouble patterns.
On a 99 model the blinking CEL means the exhaust is running rich enough to melt the cat. At least the code I know, that will make it blink.
 

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-- Is the crankshaft position sensor plugged in? I see reports that a faulty crankshaft position sensor will cause the tachometer to bounce all over the place. During a timing belt replacement job, this sensor often gets unplugged. Also its wire harness could be messed up by accident as it is so close to all the timing belt components. Maybe try running the Rav4 and wiggling the crankshaft position sensor's wires.

-- -- Since a timing belt job was just done, I would not rule out that the timing belt tension was incorrectly set, resulting in incorrect timing and possibly affecting the water pump.

-- I see a few posts here indicating that a significant air leak will cause the tachometer to bounce all over the place. Have you checked for a split or loose vacuum hose; a split or loose PCV valve hose; a loose throttle body; and similar, especially those parts that were handled during all the recent maintenance?

-- Was a proper air purge of the coolant system done? Air in the system will mess up coolant temperature signals to the ECU, for one. Everyone has their own way of doing purges. Here is what I do: With engine cold, remove the radiator cap and top off. Leave the radiator cap off. Put a pan underneath the radiator to catch run off. Start engine and rev at 2500 for five minutes. Add coolant to the radiator to keep it topped off. Gently squeeze the upper and lower radiator hoses to help get air out of them. Look for air bubbles burping out of the radiator. With engine still running, top off and put radiator cap back on. Rev for two more minutes at 2500 RPM. Fill the reservoir to the high line. In the next few days, when the the engine is cold like first thing in the morning, top off the radiator.

-- Have the two radiator fans been coming on? They are either both on or both off. If you need some basic tests of the fans, post back.

-- Just to eliminate it: Inspect the spark plugs. Are any of them oil soaked?
 

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Discussion Starter #8
@Elle_Rav4 - all items from your 2nd post were confirmed as completed prior to my post (mechanic said his air purge is the same as yours, because it's the correct way)

@Roundabout thanks for the encouragement

Updates
6.18
*Mechanic replaced ECT
*Received text from him:
I believe I have resolved the Rav4 electrical issue. I wiggled wires till pinpointed the culprit. I removed ground wires to insure a clean and solid connection. After I finished the trial and error task I ended up with a victory. I have driven it all morning and have had no issues.

6.19
I picked it up, immediately felt a difference (everything was better somehow - and radio was on - it hasn't worked since May 2018).

Between mechanic and I, RAV4 has been driven 50 miles (street and fwy) with no issues.
 
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