Ed Petry

Hi Everyone -- In the past week or so my 86 NA has started to idle very rough when first starting in the morning. I assume it is the fuel pressure as the issue goes away if I "give it some gas". Once it smooths out it is ok for the rest of the day. Any ideas on what fuel component it is? Injecters? Fuel regulator? Anti-back flow valve? Thanks in advance. Ed

Fintro11

could it possibly also be the fuel filter?

Ed Petry

Hey Fintro11 -- yes it could be the filter. I thought a clogged filter caused the engine to bog down when you hit the gas?

Ronin-951

Bet it's the DME Temp sensor, as it tells the DME if it's dealing with a cold or warm engine when selecting the fuel map. Located under the front intake manifold runner, 'Clarksgarage.com' has the specs.

ron.eddy

I would start with the simple stuff but that's just me. My '90 started idling very rough and would smooth out when warm. I did a tuneup along with the fuel filter and it runs like a top now. Of course, mine hadn't had a tuneup since the PO like 7 years ago. Conversely on my '86 I decided to go straight to the trickier stuff, replaced vacuum lines and some other things and ended up with a surging idle AND rough still! Did a tuneup on that one and it fixed the rough idle but she still surges!

John_AZ

+1 for Ronan-951

I am sure you have done the basics. A few courtesy of the WSM & TSBs.
Clean grounds, sensor connections, all electrical connection on top of the engine, battery posts and wire connections. Check for vacuum leaks especially the hoses to the ICV and the intake boot. If cracked replace.

The AFM-check to see the "door" moves freely. If not get some Gumout Fuel Injection and Throttle Body cleaner------NOT Carburator cleaner---and spray the "door" pivots.

Use the same can to squirt into the ICV directly a couple of times. The hose closest to the fuel rail is difficult to remove but possible.

Pull the vac hoses to the FPR & FPD and look carefully for gas moisture or drips. Really look close and again.

You may have an injector sticking. Maybe a can of the Chevron ULTRA SUPER fuel injection cleaner.

Pull the O2 sensor connection apart and see if it helps.

and on and on....

GL
John

Ed Petry

Thanks for the ideas and advice.

Had a bit of time over the weekend to look at a couple things and to observe the issue farther/better. Here is what I discovered.

Coolant is full. Temp is good (mid gauge when at operating temperature - cool after overnight rest)

Gas tank basically full (less than 80 miles since fill up) Fuel not an issue - problem present before fill up. Added Techron to existing fuel and topped tank off.

Need to check the rotor button.
Need to check for vacuum leak in the idle stabilizer circuitry
Need to verify fuel pressure.

Replaced DME temp sensor (attempted starting no change).
Disconnected the O2 sensor (attempted starting no change).
Turned key on and let fuel pump run for 10-15 seconds (attempted starting no change).
None of these sequences had an effect on the problem.

This appears to be an open-loop idle issue. Closed loop idle is controlled but 'something' remains. No problem at speed (fuel filter/pump not suspect)


After sitting overnight:
Engine will start but dies.
Restart results in rough idle -- hunting -- 500 to 1500 rpm
Hunting continues for 2 minutes and then starts to smooth out.
After 5 minutes driving -- idle has smoothed and engine is idling at 950rpm or so.
Idle continues to have a roughness not present prior.

If the throttle is cracked a bit (idle held @ 1100 rpm or higher) when first attempting to start, the engine will stay running.

Any help is appreciated.

Cheers
Ed

Ed Petry

Hey John_AZ,
Thanks for the advice. Good suggestions -- will look into those items. One question - The Gumout website doesn't show Gumout Fuel Injection and Throttle Body cleaner as a current product. Do you know where one can get a can of it?

John_AZ

Your right, I checked the Gumout page and it is now obsolete. Some online still stock but not worth the shipping cost. Part 7490.

Try to get any brand cleaner that is specific for Fuel Injected engines--Air Intake & Throttle Body Cleaner.

I cannot remember where I picked it up. Auto Zone, O'Reilly (Checker) or Pep Boys are close to me??

GL
John

Ronin-951

Sorry the DME temp sensor didn't do it for you, fits the profile perfectly ... and was an easy repair. Guess chasing vacuum is the next best bet with a look-see at the ISV - known to crack. I would replace all the vac lines, no matter the condition, if the intake was coming off during inspection. I never really noticed much improvement of anything when using Gumout, but 'Seafoam', [Availible at NAPA] is some GREAT stuff!

bigcigarjeff

you might try doing the FRWILK trick of basically turning off the throttle position sensor/switch that is below the throttle body..which I did because I was having the same problem and now my car runs smooth as silk..since you have a na car this will be easy to do. Do not disconnet the plug from the switch..on the throttle body, top left there is a little screw with a nut on it at the throttle body...get a little wrench and undue the nut ..not all the way off..all while keeping the screw from turning, just hold wiht small screw driver...now make sure it's quiet where your working because you will need to be able to hear the little click the throttle position sensor makes..so now your going to turn the screw til you hear the click..you can experiment a little by turning it back and forth so you hear the clicking of the switch..adjust so that you have turned the screw enough to hear the click and about a hair past that..hold that position and tighten down the nut--don't go crazy...basically you have just opened the butterfly valve in the throttle body a little tiny bit...start it up..you may have a high idle and just turn the idle speed screw on the top..I think 7mm socket fits in there..look at you rpm gauge and set it to about 1000 rpm...it may sound high but it will smooth you out like nobodys business and no more boggin down when you turn on the ac...I swear by this little trick...So this little trick basically turns off the momentary fuel cutoff at about 1600 rpm..so driving around you will notice that the rpms don't drop as quick as they normally do with the switch in the on/off position..Let me know if you need more help..if anything you can tell if your TPS is working or not working...I even replaced the TPS last year with no effect on the first start up bad idle til warmed up...I'm thinking now that it may be the wiring...one day I will check it but I like my idle the way it is....I will try and find the FRWILK tutorial on this procedure...

bigcigarjeff

http://www.the944.com/shudderm.htm

Ed Petry

Hi Everyone,
Found a source for Throttle Body cleaner (in a spray - VOE complient). Made by CRC and sold locally at many parts stores. Have used CRC chemicals in electronic repair for years so I trust their product line in that regard. Busy this week and most of next (repairing son's car). Will let everyone know how the CRC works. Thanks for the advice and help. Cheers Ed

Ronin-951

Would like to re-emphasize the use of Seafoam gas additive, you need to clean the 'inside' of the fuel system - nasty dried ethenol build-up can muck up the injectors, not that you have that problem - runs well when warm - just saying. Might want to spray some starting fluid at suspect vacuum areas and listen for engine reaction too.

Ed Petry

Hi Everyone,
Thanks for the advice and thoughts.
Ronin-951 -- Yes Seafoam is great. Every year put the car to "bed" with a can of Seafoam. Makes the spring wake-up much easier.

Finally had time to investigate everything. The rotor cap and button were good. Plugs needed a slight adjustment. Then grabbed the can of brake cleaner (Acetone) and started spraying the vacuum lines. Sure enough, under the manifold....near the ICV the car smoothed out and the idle stablized. So, the vacuum leak is basically isolated and is close to being fixed. Did not fix exactly which vacuum hose or part is the problem but feel a lot better about the fix.

Thanks to you all for your advice and comments and general P-car stuff.

Will let everyone know what ends up fixing the issue.

Just in the Bay area for the weekend and loved seeing so many P-cars just driving around. Lucky group of people.