erubin Posted November 28, 2005 Share Posted November 28, 2005 The car is a '93 GS300 (inline 6cyl) with 140K miles. The car has been well maintained. The spark plugs (Denso Iridium), wires and cap/rotor were replaced a few months ago. The car runs rough as though the EGR was always open or that a few cylinders were not running. This problem is with the car hot or cold, at idle or under load. No check engine light even though this has been going on for a week. I even put the diagnostic into blink mode but nothing stored. I put my timing gun on each wire one by one. They all fire regularly. I put a NOID light on 4 out of 6 injectors (couldnt get to two injectors under the throttle body) and the light flashes regularly. I put vacuum on the EGR valve and it opened and the engine runs just a bit more rough. i took off the EGR (not too dirty with carbon) and bench tested it, it opens and closes with my hand held pump. I did a block leak test (sniffs for exhaust in the coolant and changes color if positive) but came up negative I disconnected and reconnected the MAF sensor several times and the engine does not change a bit (I would expect a change in regime but maybe the fundamental problem is masking it). But if the MAF was bad I would expect a check engine light I would think. Furthermore I'm not sure if the MAF is used in open loop and I have the problem even with a cold engine. I checked the engine timing. It is at 20 BTDC with and without the diagnostic jumper installed. It should be 10BTDC with connector and 7-19BTDC (varying) without it connected. I rotated the distributor as far as possible and brought the timing to 16BTDC, still way over spec. I removed the upper timing belt cover, rotated the engine to TDC and the cams line up perfect (so belt did not skip). What should I test. Help! Quote Link to comment Share on other sites More sharing options...
monarch Posted November 28, 2005 Share Posted November 28, 2005 When did the symptoms start? Out of the blue or were they there when you purchased the car? If the timing doesn't change with the diagnostic jumper installed the TPS (throttle position sensor) is may be faulty or improperly adjusted. Normally the TPS is extremely durable and doesn't need adjusting, but sometimes owners or mechanics inadvertently mess them up while working on other components in the engine compartment. A hole or loose clamp in the tubing that runs from the throttle body to the air filter can cause a rough idle. Quote Link to comment Share on other sites More sharing options...
viclykewhoa Posted December 2, 2005 Share Posted December 2, 2005 You sound very knowledgeable. I hope you get your rough idle problem fixed. I have a similar problem. How do you check the timing and what is BTDC? The car is a '93 GS300 (inline 6cyl) with 140K miles.The car has been well maintained. The spark plugs (Denso Iridium), wires and cap/rotor were replaced a few months ago. The car runs rough as though the EGR was always open or that a few cylinders were not running. This problem is with the car hot or cold, at idle or under load. No check engine light even though this has been going on for a week. I even put the diagnostic into blink mode but nothing stored. I put my timing gun on each wire one by one. They all fire regularly. I put a NOID light on 4 out of 6 injectors (couldnt get to two injectors under the throttle body) and the light flashes regularly. I put vacuum on the EGR valve and it opened and the engine runs just a bit more rough. i took off the EGR (not too dirty with carbon) and bench tested it, it opens and closes with my hand held pump. I did a block leak test (sniffs for exhaust in the coolant and changes color if positive) but came up negative I disconnected and reconnected the MAF sensor several times and the engine does not change a bit (I would expect a change in regime but maybe the fundamental problem is masking it). But if the MAF was bad I would expect a check engine light I would think. Furthermore I'm not sure if the MAF is used in open loop and I have the problem even with a cold engine. I checked the engine timing. It is at 20 BTDC with and without the diagnostic jumper installed. It should be 10BTDC with connector and 7-19BTDC (varying) without it connected. I rotated the distributor as far as possible and brought the timing to 16BTDC, still way over spec. I removed the upper timing belt cover, rotated the engine to TDC and the cams line up perfect (so belt did not skip). What should I test. Help! ← Quote Link to comment Share on other sites More sharing options...
mehullica Posted December 2, 2005 Share Posted December 2, 2005 Have you pulled the plugs and checked them for discoloration? Possible cracked head or head gasket? Quote Link to comment Share on other sites More sharing options...
TurboGS300 Posted December 2, 2005 Share Posted December 2, 2005 I'd check temp sensor since there's no change from hot to cold. <_< Quote Link to comment Share on other sites More sharing options...
erubin Posted August 29, 2006 Author Share Posted August 29, 2006 It's only fair to give a finalee to the story. Although my friend said the spark plugs were recently changed it turns out that they were in terrible shape so in fact he paid a mechanic for this work and it wasn't done. the number 6 spark plug was particularly bad and was cuasing lots of poor firing. Didn't show up as a check engine light, I guess they weren't as sufisticated pre OBDII regarding misfire detection. Replaced all the plugs and problem fixed. Quote Link to comment Share on other sites More sharing options...
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