Hi, I have a Non-torbo 87' supra and for some reason it just keeps reving up and down 500-1500 rpm. The exhaust burns my eyes so i suspect it running very lean. I'm not sure whats wrong. Also it has been sitting for a few years. What should I do?
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Sounds as if the engine is running rich ( over fueled ). There are many reasons for this issue. I'm suspecting the vehicle is fuel injected? You can check for a leaky fuel pressure regulator on the fuel rail and also a sticky/stuck EGR valve that can cause this problem. These are the quickest and easiest checks to do first. IF all ok, you may require the use of a scan tool to check sensors/codes for proper operation and look at any available data stream that may point you in the right direction
Before we both knock ourselves out with fuel injector testing. Hook up a Digital voltmeter (DVM) to upstream O2 sensor and lets see how she is burning. Remember positive lead of DVM to signal wire and negative lead to ground. Anything above 550 mV is rich anything below 350mV is lean. Be mindful that an exhaust leak the size of a pin hole in this region can cause a rough idle. A healthy reading should bounce between 550mV and 350 mV.
Next to test is O2 is working block off air in take making mixture rich and see what O2 says about it . Then pull off a vacuum hose (a lean condition) and see if DVM drops to 200to 300mV's.
Keep me posted.
Afew things to check first before you start playing with it is to take out the air filter if dirty replace it ,Chrck the exhaust and see if its carboned up if so burn it over a fire and then tap it to remove all black carbon Then check the carby again as all carbys have a mixture screw and a air vent screw and check the compression to make sure the plug is caused by
richness and not oil.
Also check the engine breather pipe as a blocked pipe can cause the same thing.
Let me know how you get on Ron
1987 non-turbo: 10 deg Before Top Dead Center (BTDC) @700 rpm 1987 Turbo: 10 deg BTDC @650 rpm.
To set the timing, you will need to connect a jumper wire between terminals E1 and TE1 on the diagnostic terminal. This diagnostic terminal is located just aft of the engine compartment fuse box. It is a black plastic box marked "diagnostic" on the cover, which flips open to reveal the terminals inside. There is a diagram on the inside of the cover which explains the terminal positions. On the Turbo model, you need to remove the forward section of the engine cover to gain access to the number one spark plug wire.