I just got an '89 Formula 350 that's mostly stock except for some new/rebuilt goodies, and I have decided that I want to restore the car to a basically stock configuration as I am not interested in racing it. It's a high mileage car (224,300+) and while much of it was taken good care of, I'm sure there is some equipment left that's past its sell by date. I am solving my problems with the car one at a time, and the guidance of you all here has been invaluable since I am a relative mechanical idiot! Here's my lastest puzzle.

I just recently solved a rich condition by installing new Bosch 22 lb/hr fuel injectors. The previous owner was running injectors that were too big without upgrading either the PROM or the rest of the intake, so obviously I was running rich before. I was also having a minor problem with low-RPM bogging and a slight idle hunt. I notice that my other problems caused by the oversized injectors have been solved (gasoline smell, poor mileage, severe bogging, etc.) but a slight low-RPM bog and idle hunt remain, although they are not near as bad as they used to be. Bogging occurs in this very narrow range between 1200-1400 RPMs and is only noticeable when I drive very slowly. The idle hunt is very slight, and is only really noticeable when the car is cold. The tach will gently seek back and forth between 800-1000 RPMs. Once it has warmed up and idled down to about 600, it idles smoothly.

The question: What should I check first in trying to solve these two problems?

1. Could it be fouled plugs? My car ran rich for about 400 miles. I have not pulled the plugs yet to see how bad they look, but if they are fouled from excessive fuel, could this cause the bogging and idle hunting? I will say that the plugs were installed brand-new around the same time the previous owner put those oversized injectors on. They're Bosch Platinums.

2. Could it be a bad O2 sensor?

3. Could it be the IAC valve?

4. Anything else you would suggest or recommend checking?

I'm new to this whole game so I have very few tools (I am acquiring equipment as we speak, in fact), no scan tool, no fuel press gauge, etc...and I live in an old retirement town where everybody I know drives a Lexus and doesn't own any automotive tools. Right now I'm just looking for general strategies of things I should check, so that I can at least learn the "why" behind things until I get the equipment to do something about it.

To reiterate, the bogging and idle hunting are both very minor, they aren't precluding me from driving the car, but the bogging does get a little annoying when I drive home through my subdivision because the car wants to surge a little bit all the time; it hovers right around the bogging point at 25-30 miles an hour. All the old folks peer out their windows and sneer at the young punk driving that loud black...THING down their peaceful street.

Anyway, thanks in advance for any advice! :hail:

 

I should add that this morning, after the car had sat overnight, I started it up and after cranking for several seconds, it fired up -- but immediately wanted to stall. I gave it some gas, and the car shook and hesitated for a moment, then it roared up to about 2500 RPMs, settled back down, and wanted to stall again.

I kept doing this for a minute and it wasn't getting any better, so I decided to just stop giving it gas and see what happened. It idled way down, practically stalling altogether for a few seconds, then suddenly it revved right up to 1000 RPMs and idled there, perfectly normally. It was 100% fine after that, with the exception of the problems I mentioned in my last post, of course.

I ran it for a few minutes, then shut it down and came back a couple hours later -- it started up perfectly normally, albeit after several seconds of cranking.

I opened the hood while it was running and heard what sounded like a barely-audible, constant hiss of air escaping. Could it be a vacuum leak? Would that cause the trouble?

 

First thing is to disconnect the battery, reset the ecm, then drive a bit and retrive stored codes, if no codes and the same stuff occurs...


As a matter of precaution, at least look at the plugs., but may as well replace them while you have them out. I'm not a fan of the Bosch plugs, but that's JMO.

I'd also replace the O2 sensor..just from it running so rich before...but has nothing to do with your cold start idle hunting.

You should also remove the TB, get a gasket set for it, take it completely apart and clean all passages with carb cleaner (spray on stuff works fine) and a tooth brush...might need a pipe cleaner too. Make sure you clean the IAC pintle as well for anything stuck on it.

After that, I'd put it all back together, check min idle speed, set the TPS and IAC and see how she does, if you still have problems, I'd suggest plugging into the ALDL and monitoring...good reason to buy (or make) a scantool.

 

Thanks 8Mike9 -- which plugs do you recommend? I've heard the AC Delco RapidFires praised here before.

Your other suggestions sound like good ideas and I'll start checking all of that out. Is there anything I need to do to reset the ECM besides leave the battery disconnected for a while? I'm intending to get a scantool for sure...it provides access to such a wealth of valuable data when you're trying to troubleshoot stuff.

BTW, any thoughts on the vacuum leak idea? Could that cause at least some of these problems?

 

Re: Plugs...I like the stock AC's...R44TS or R45TS???don't recall the number.

Disconnecting the battery is all that's needed, just a minute or so, although some say 15 minutes, not sure why, but what the heck.

Vacuum leak cold be an issue, but I'd be wondering how it (ECM) control) cwould compensate once warmed up (if I'm interpeting things correctly) and idle so low (600rpms) when Idle speed should be 700-750.

If you really suspect a vacuum leak, there's many ways to check it, carb cleaner, propane...my favorite is water in a 409 bottle and listen for rpms to drop when the water temporarily drops the idle...doesn't last as long as a raised idle from carb cleaner, etc, but safer and cleaner IMO, and doesn't stink as much either

Scantool is definitely a good idea, especially with the milage on your ride, best to spend a few buck on diag equiptment, than swap unnecessar parts "just because".

Scantool will show you MAF start up info, CTS info, IAC counts, etc, etc, all which could be a clue to your problem.

 

Thanks for the tips on how to check for vac leaks. I believe I misspoke about the idle speed -- it does idle at around 750 RPMs; I was accidentally thinking 600 because that's where it drops down to when you put it in gear and the park/neutral switch trips. Of course, as I mentioned, when it's idling it wanders around a bit.

I'll spend some time tomorrow trying a bunch of this stuff and report back if I find anything significant.