1987 Toyota van, manual trans, 4X4
A couple of weeks ago it was time to renew my tags and that meant taking it for emissions testing. For day-to-day use I do not have a catalytic converter installed. I have a piece of straight pipe so I had to reinstall the catalytic converter for testing. The van passed emissions just fine but I did not swap in the straight pipe right away. About that time the van began having an RPM dip and/or wanting to stall at stoplights but only when the engine is warmed to operating temperature. The RPM dip/stall was more severe the more rapidly I decelerated. Also the stall/RPM dip is more pronounced when stopping pointing downhill and less when pointed uphill. I inspected the vacuum and air hoses and they are all in good condition. I shorted the diagnostic plug and the computer gave me a code 11, throttle position sensor. I went to the junkyard, found another throttle position sensor, took it home tested that it was good with a multimeter and installed it. I removed the old TPS and it tested bad in the idle position. (on a side note these TPS’s are very serviceable! Just pop the cap off and sand the contacts!) Installed the replacement, cleared the code and went for a test drive. The damn problem still existed though it seemed a little less severe. I checked to see if the computer was giving a new code but the computer says everything is fine. Today I removed the cat and reinstalled my straight pipe and went for a test drive. Again improvement but not complete resolution. Before the problem arose, at operating temperature the van was idling at a factory perfect 700 RPM. Currently at operating temperature the van is idling at 600 RPM and at a rapid stop momentarily dips to about 400 with just a hint of a sputter. Anybody with a similar experience and/or suggestions?