Erratic idling

[doctorpws2004]

Hello all,

Just joined and am so glad to see such an excellent forum with very knowledgable people contributing. I've had an '86 Graduate for the past 4 years and have recently noted that when I start the car after a few minutes of warming up, it will rev up then down. It cycles like this until it has completely warmed up, then no further problems. Have tightened all hoses, run Techron through twice and it still continues. Not exactly an expert on the L-Jetronic system, so I am wondering if this is the source of the "problem". Doesn't stop me from driving or enjoying the car, just kind of wondering what the heck is going on. Any suggestions?

[desert spider]

Have you also tightened the hose clamps on the large rubber cross-over pipe (aka middle air hose)? If so, you may also want to check both fuel filters, although I would expect that,if dirty, they'd give you a problem while driving. You should also check the temperature sensor. If it is o.k., it will read 200 to 400 ohms at 176 degrees F and less than 200 ohms at 185+ degrees F. My "84 Spider runs fine, but even I get a little wavering of the idle speed on start-up up. But the waver is no more than 100 rpm or so, with the nominal idle at 950 rpm.
Jim
'84 Spider Veloce

[papajam]

Welcome to the Alfa BB, Paul!
I'm not an L-Jet expert either but the first thing I'd check for is a vacuum leak followed by clean and tight electrical connectors.

[desert spider]

Come to think of it, vacuum hose leak is a very good suggestion. That did happen to me several months ago and the result was a very lopey idle. On the L-jetronic, the vacuum hose attaches low and to the rear of the intake plenum chamber (on the right side btween the plenum chamber and the firewall).
Jim
'84 Spider Veloce

[John M]

Hey Paul:

It does sound like a small vacuum leak. Make sure that flexible rubber hose that runs from the air flow meter to the hard plastic intake hose is not cracked or torn. Also, make sure the lip of the hard plastic intake hose where it joins the flexible rubber hose is not cracked. Both run over the top of the cylinder head and are prone to problems. Its very common for the hard intake hose to crack at the union between itself and the flexible hose. Don't overtighten at this union.

After looking at the manual for troubleshooting, the irratic idle on warmup may also be seen with difficulty in starting when hot or cold.

Other possibilities include a failing cold start injector, loose electrical connection on one of the fuel management devices, or a failing auxillary air device.

Best Regards,
John M

[gotglasses]

Check the auxiliary air valve. So long as it is only a few hundred RPM bounce it is OK. If you get a huge difference like a 1000 to 3000 rpm you have serious computer module/ecm trouble.

Here's a good site for troublesooting list:

http://www.alfaclub.org/techstff/boschfi.htm#badcold