At Odds with a Nissan

Hey All - Several of you were GREAT with info to repair my son's Saab, hoping I can get help with a mystery with my Sentra. I have a 1987 Sentra XE with a E16i (throttle body injected), 5 spd. About two weeks ago I noticed the idle running up at about 1000 rpm. Then earlier this week it jumped up to 1200-1300 rpm at idle - with the tack needle wavering up and down about 50 rpm. Ran good otherwise, just idling high. Finally got it into the garage this afternoon for a look see. I figured it was a vacume leak, but all hoses are in good condition, nor could I hear a tell-tale hiss. Also nothing registered in the ECU when I checked it. Two odd things occured while I was tinkering around. 1) As I would lift the air cleaner housing the rpm's would drop momentarily, then pick back up to 12-1300 again. 2) As the cooling fan would come on the rpms would drop so low that the engine would almost stall, then run right back up once the fan cut off. Been reading my manual but can't draw any conclusions. Plan on doing the Carb cleaner test tomorrow to better look for vac leaks (didn't have any today). Otherwise, just not sure. Any ideas???

does this engine have a conventional distibutor? could be an advance mechanism failure. Also the mention of the idle dropping to the point of nearly stalling sugest to me an electrical problem; the added load of the fan switching on is bringing out a weakness in something.

In reply to HappyAndy: Not sure on the spcs for the distributor. Could not find a vacume line to it so I figured it was controled by the ECU. I forgot to mention I did replace the O2 sensor with no change. Also, the injector seamed really noisy - kind of rattly - any chance it may have just reached a point of being worn out and spraying too much fuel to cause this?

In reply to Pinto7: I doubt that worn out injectors would cause the problems that you are describing, but a faulty distributor or ignition component, mechanical or solid state might. Also, I didn't think of this until just now, but does this engine have some kind of IAC valve to controll the idle speed? I am not all that familiar with TB injection systems, but all the multipoint systems that I know of that don't have an electronicly contolled throttle valve do have some sort of IAC valve to help regulate the idle speed, that could be sticking from years of carbon reside or just worn out. There is also probably a coolant temp sensor (seperate from the one that operates the gauge or warning light )that sends a signal to the ecm, if the ecm doesn't see that signal due to a bed sensor or corroded connection it will think the engine is stone cold and make it run rich/ high idle to warm it up.

BTW, what was the outcome/final diagnosis with the SAAB?

My 87 pu had a nasty little thing called a wax valve. When it goes bad, your car gets stuck with the choke on. Could be the problem.

In reply to HappyAndy I do remember you responded to the Saab issue. Thank you. Haven't had opportunity to repair yet, due to weather and money getting tighter. But I think I have the information to effect repairs as I locate/purchase the parts. As for the Nissan, it has a lot of abreviated components in this area. I don't see one marked as IAC(?). I see Temp Sensor Idle Compensator, a Thermal Vacume Valve (wax type mentioned in the post by OpusDork) part of the EGR system. I May look at the water Temp Sensor you mentioned. Hopefully it is cheap to replace. May look at the TVV too. Any other info/ideas would be great. You fellas are really helpful and I really really appreciate it.

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Something quick and easy to check-top off the radiator and puke. I've had similar symptoms if various vehicles. Thet were trying to purge an air bubble out of the coolant system.

In reply to HappyAndy: Good News I think. Took the info from all the posts here and spent some time at the local junk yard and sourced a decent temp sensor from what looked like a decently kept up Sentra. Swaped it out, worked with a few adjustments, and burped the cooling system. The RPM's were steady at about 850-900. Still a little high, but livable for the moment. I did discover a hairline crack in the head. Guess I'll start my quest to replace the whole thing now. Any one looking to get rid of a decent E16i motor or head really cheap (like free?) Thanks a TON for your continued assistance.