I have a 305 TPI motor. Fuel pressure is good. New IAC valve installed and reset. Injectors checked and good. Starts and runs as expected expect a couple things I am not sure if they are issues or not.

When the car warms up it idles around 600-700. Hard for me to tell exactly. If I snap the throttle off idle it has a slight dead spot off idle. If I open up to say 800-900 and snap throttle no hesitation. If I put it in gear for a few seconds and then back to park and snap throttle no hesitation off idle. Am I expecting too much? Should you be able to snap the throttle off idle with no hesitation?

Other thing I noticed with the idle when coming to stop signs. If I pull up to a stop sign idle goes to 600-700 as expected and holds. If I leave within 10 seconds or so isle stays at 600-700. If I stop and have to sit there for a minute or two. The idle goes to 600-700 then after 15-30 seconds it drops to 500. You can throw it into neutral or park and it will go to 600-700.

Are these two related? Let me know your thoughts.if you have had this problem and figured out what was wrong.

 

What year?

What is the status of your tune up items (Age/Miles on Plugs, wires, cap/rotor), when was the last time you cleaned out the IAC passage and your throttle body? Have you performed the IAC Rest/Min idle set procedure? Have you checked base timing? Are you scanning data from the ECM? Does your CTS show values that make sense? Do you have any modifications?

 

This is an 86. Has 29000 miles on it. All stock original. I put new plugs and new IAC valve. When I installed IAC valve I did the key on disconnect IAC reset. Is there something more than that needed? Base timing was 5.5. I know 6 is recommended but didnt think 0.5 degrees of timing was an issue as I didnt have a distributor wrench. I dont have any ECM scanning tools. Throttle body and IAC passage was cleaned when I replaced the IAC. What does CTS stand for?

 

CTS = Coolant Temperature Sensor. This tells the ECM what temp the coolant (Engine) is operating at and affects it's mixture.

86 is a MAF car. I could suggest unplugging your MAF and seeing if anything changes. It's a basic and dumb check, but if your car runs better without it, may be time to replace. It is very hard to really test a MAF.

In the lack of being able to scan (If you have a lap top around you are a cable and some free software away from reading data), you need to pull a plug an see what it tells you (Rich/Lean?).

Have you checked Fuel Pressure and done a leak down test? Check the regulators response to vacuum drop. When you snap the throttle, pressure should jump up. You may have a leaky injector.

9th injector may also be stuck on causing a rich condition. It works on a thermo switch only, no ECM control.

I agree 1/2 of a degree shouldn't be a big issue, but a distributor wrench is like $10... get one.

I like to do the IAC reset procedure focusing on IAC counts. I follow the instructions, but in the end I end up adjusting the throttle stop screw just a bit more to get my warm idle in P at ~750RPMs with the IAC at around 20 or so counts. Obviously you need to be able to see ECM data to do this.

There is some basic stuff that can be checked/eliminated.

 

Fuel pump and FPR are new. All checks are good there.Tested for leaky injectors. Had the rail out with pump on and no leaks in any of them including the 9th injector.

I unplugged the MAF and it started hard but ran about the same. May have had slightly more punch but may be my imagination. It definitely didnt change the idle at stop signs issues. Still falls slightly after long stops. Idle was slightly lower with it unplugged in gear. Maybe around 500 rpm. Still had the off idle dead spot when snapping throttle. Its very slight. This isnt a major dead spot. Should it be able to rev without any hesitation whatsoever with a hard snap at idle?

I cant move the throttle stop screw to increase warm idle RPM to 750 without monitoring the IAC data? Warm idle in park is 650-700 maybe. In gear is is 500-600.

 

Ive seen two methods for resetting the IAC. One said turn key to on and unplug IAC. Turn key off and plug back in. Another one said jump A B in aldl then key on and disconnect. Shoudl A B be jumped to put car in service mode to reset the IAC or doesnt matter?

 

Jumping the terminals forces it closed. Then if you go unplug it before you start the car, you know it is completely closed.

No, you do not have to monitor the IAC counts to perform the procedure. It's just an added step I like to do after performing it, and then you can open the throttle a bit more to reduce how far the IAC is open. The IAC will operate to achieve the ECM's called for RPM. Think of looking at the IAC counts as a measurement of how accurate you set the throttle screw. It does not have to be perfect to operate.

While the 9th injector isn't leaking, it doesn't mean the thermo switch isn't bad and hanging it open leaving you rich and bogging at the snap of the throttle until air velocity catches up. The ECM already has a power enrichment mode to go into after % of throttle is used. If the ninth injector is being told to stay open, you would be too rich. If everything else seems to be operating properly, this often gets overlooked.

Would be nice to see a scan of what you car does. But without it, all you can do it start eliminating possibilities.

How about your O2 sensor?

 

Search the archives for "throttle tip in hesitation" and you may find more information.

 

Im sure it is lean and not rich. Two reasons I say this. One is my experience with my race engines using carbs. When I have had clogged nozzles for the accelerators pumps you dont get fuel when you open butterflies which results in an off idle hesitation. When you snap open throttle you add a bunch or air without fuel it will be dead. If it was rich it would snap right up.

Second reason I say lean is I have noticed when I put it in gear, the rpms drop to 500 like I said. Then put it back in park and snap the throttle and no hesitation. Put it in gear seems to be causing it to richen dropping the rpm.

My question on setting the idle with the throttle stop screw. If the ECM is targeting a specified rpm wouldnt the ECM override whatever you set with this screw and IAC disconnected after you reconnect the IAC?

Wouldnt a bad O2 throw some sort of code? I dont want to do the throw every part at it approach. There has to be someone with experience with these TPI motors that knows what is causing my problem.

 

No, lazy aged 02's don't always cause a code

Yes the IAC overrides and takes control. You want it to, it is the goal of the whole procedure. You set the minimum idle warm below the target RPM. With the IAC unplugged you should be around 600 RPMs or so, Once the IAC is plugged back in, it will open up to achieve the ~750RPM or so the ECM wants to see. There will be an associated number of counts (or steps) the IAC will open to achieve this. Back the screw off a bit more to let the blades close and counts will go up to compensate. Open the plates a bit more with the screw and the counts will go down to compensate. I like to see the counts low so I know the IAC isn't using a lot of it's travel to control the idle. Giving it plenty of travel to control the idle, but there is no hard number that must be achieved.

 

Set to 600 rpm in park or in drive?

 

Ok so I figured out some things tonight. I did the IAC reset, Tried to set the base idle with IAC unplugged and it was way too low. It wouldnt even idle. When I turned the idle screw I finally got it to idle around 400. I adjusted it to 600. Then reset the TPS back to 0.540V. Car now idles around 750 in park and 550-600 in gear. Main thing is it steady in gear at stop signs.

I am guessing what was happening was when I came to a stop the IAC tried to close and idle on the base idle screw setting. Since mine was too low the ECU would try to open IAC to compensate causing the idle to hunt around. Now that the base idle is right it doesnt have to use the IAC to raise it causing the rpm fluctuations. At stop signs I can sit there forever and the idle is stable and right.

 

Sounds good. I am not sure how quickly the IAC can move TBH, I just know I like it to move off seated (closed) as little as possible and what you are describing I could say it this way: It can get to to 20 counts sooner than 150 from 0 (Closed). Certainly then I would think it would make a smoother transition from part throttle to IAC controlling idle speed the less counts (Steps) it needs to make

The bigger question is, did it do anything to help your hesitation?

 

It has a slight hesitation if you snap it open real hard. If you just open throttle normal it does great. I went through the gears and it had plenty of punch. I have to open throttle pretty quick then it has that hesitation with what sounds like some pinging, maybe? Base timing is 6. Could lack of ECU timing advance during this snapping of TB cause the hesitation? If yes, other than checking base timing what else could be checked with timing? Just dont see how the system could react fast enough to add fuel through injectors when you snap open throttle. Seems to me the system would have to run rich at idle to allow a quick snap of the throttle open, no?

Also got me thinking.....If the TPS is a voltage that tells the ECU how open the throttle body is open then couldnt you manipulate this? Meaning if the idle screw is set to have a park idle of 750 rpms and you set TPS sensor to 560 or 580 wouldnt the ECU think throttle is farther open then it is and be adding more fuel? Thus help the hesitation. Probable someone will tell me why this is not true but got me thinking if it would work.

 

What type of injectors? Not leaking does not mean they are working OK. If Multecs, that's the likely problem. Low RPM PW and spray pattern is not good. You can try increasing the idle voltage PW offsets but that will likely require reducing other fueling items if idle is too rich.

 

I am not sure of the actual processor speed in an 86, but I am sure it is a lot faster than you give it credit for. Someone here probably knows but it is probably 2,4,or 6 Mhz. Hz being cycles per second and Mega meaning millions. So it is doing a million cycles per second to crunch data. It will do a fine job of getting your timing there.

The injectors are controlled by electrical pulses that open them. Very fine pulses that are very accurate. The short coming in your factory fuel system is actually the injectors. They will be what could be slowing down, not the computer system. As said above, just because they are not leaking doesn't mean they are in perfect health. Have you checked the Ohms on them hot and cold? Are they pretty balanced across all 8?

The ECM using the TPS for a few things and can really throw the system for a loop if it is not getting proper readings. The car from the factory was designed to operate with a smooth transition from .54V to 4.6V (Anythin over is just gravy, once it sees it's threshold voltage it considers the car at WOT). Power enrichment mode is actually engaged (the mode that gives you an extra volume of fuel) based of a % of movement. I say that to say this. If you are having to adjust the TPS to get your car to run better you either have a bad TPS or you have other issues that you are covering up. The ECM does not add fuel just based off the TPS alone. Ultimately, in closed loop, it will get feedback from the 02sensor and just trim the fuel back down to where its target AFR is.

Have you searched much on this issue as suggested?
Have you thought about setting up something to read ECM data?

This is not a carbed motor. The ECM can tell you exactly what it is seeing. You don't have to guess if you are rich or lean. You can go beyond just reading the plugs and actually see under different conditions what is going on. More from the BLMs than the 02 sensor. However, you should still look at your plugs, they tell a lot.

You said "Someone that knows these motors should be able to tell me what my issue is". The problem is you have no data. As Vader said, there is a lot of info here to read through. Could be a few different issues and it needs to have troubleshooting done. As 84 Elky mentioned, I would consider your injectors suspect. Especially if they are original. their seals were not designed with today's ethanol fuels in mind. They may not have a static leak, but years of deposits, worn seals, and ageing coils could have your fuel control all over the map cylinder to cylinder. They are not as good as today's injectors. One thing I can assure you, you will not find a forum or group that has a better knowledge of your car bumper to bumper than here.

SouthBay is a good place to get them cleaned and tested before you just replace them.

 

The bad injector thing is posted every time someone posts any problems whatsoever. The factory ones obviously worked fine when new. Maybe they do have problems down the road but I do know this. I changed my original injectors to Bosch injectors as everyone on here says is the cure all. It didnt fix any of my problems but it did cause a new one. After installing the new Bosch injectors it threw lean codes which it never did with the original ones. I assumed there was no way the new injectors were the cause so I chased the lean code cause for 2 months before deciding to go back to the original injectors. After reinstalling the original injectors the lean code went away. The help seems to be pushing products at times rather than troubleshooting the specific symptoms that are posted. Almost every post someone makes gets a reply to buy Southbay injectors. If injectors are bad how can it run great during all driving situations expect an off idle snap of throttle in park?

I would love to get data but its not that easy. No one around me has the ability to hook up and read this older system. I did take it to one place local and asked them to look at fuel trims. They called me later in the day and said it was done. I asked what did they see. I was told its "good". They charged me nothing which tells me they didnt even do it. I could buy a cord and install software but I read if you dont know what youre doing you can fry your ECU. Is this true? What does this mean? Maybe thats not true but I dont know how to collect or read the data if i had the cord. I was trying to make it like new but I dont want to shotgun changes based on guesses. I know youre saying if there was data maybe someone could help. I agree but not sure how to collect it and read it. Whole thing is frustrating.

 

WOW!
This is not a post I want to make, but your post really set me off. Your tone appears to be: Just give me the answer I want so I can fix my problem and go way.

Regarding "the bad injector thing":No one here is pushing product as they have no financial interest. Improperly functioning injectors, combined with an improperly functioning fuel pump, are the major causes of tip-in hesitation, poor low throttle response, stumbling, etc. That's why it's suggested as something to review. You can certainly reject the suggestion, but don't berate those recommending it.

Regarding installing Bosch and running lean. That's virtually impossible unless a bad install, faulty injectors, improper flow rate, tuning has changed, etc. Why? Because Bosch's provide so much more fuel and provide it much more efficiently than Multecs due to the superior spray pattern. The normal problem is running pig rich, especially at idle. Personal experience plus hundreds of posts on this site confirm it.

Regarding "not getting data". Have you tried? Have you read the stickies on the DIY PROM thread of this site? Particularly: https://www.thirdgen.org/forums/diy-...uide-book.html. Have you gone to www.moates.net or called them to understand what's needed? Have you investigated using TunerCat or TunerPro? The answers are likely no based on your post. No one here is going to spoon-feed you. You have to have some skin in the game. Can't solve a problem without data. No one here is sitting in your driver seat experiencing what you are. Get what's needed to get the needed data and post a log. Then and only then can objective help be provided. Read and learn. And BTW, you can't fry your ECM.

 

I do t know what year your 305 is but this might apply
http://www.gmtips.com/3rd-degree/dox/tips/ecm/prom.htm
for a aldl to usb cable look at moates xtreme aldl or 1320s cable.

http://www.1320electronics.com/products.html

http://www.moates.net/aldu1-and-cabl....html?cPath=64

 

It's because components wear, they were not designed for today's fuel, and it has been proven to be a weak link... well if you think something failing after 30 years is weak. Everything worked well on your car when it was new, nothing last forever. Nobody is telling you to change flow rates, Ohms, or anything else about the injector, just to replace a worn failing part.

Very few members here will tell you anything is a cure all. I researched them as they were in my car when I bought it. What I have found is the exact opposite of what you say. I have found members that need some tuning done with the Bosch 3's to settle the idle out mainly. Don't confuse someone saying it runs great as a statement that it is optimized. All depends on what you find acceptable. You may not know how bad their car was running before the swapped them. Perception is not the same as recorded data.

Based off this thread it's because you want someone who has not driven, rode in, or seen your car to tell you what is wrong with it. This usually results in throwing parts at it. This is why in a lot of threads you will see people asking for data logs. It's data, not perception.

That is totally untrue. That is where you are ending up because you don't want to take other suggestions on troubleshooting. You push for answers on what needs to be replaced. Also, specifically I said -

Which is not pushing product at all, I told you to have them tested. SouthBay is a long time supporter of this board and take care of us by offering us a discount. Additionally, he doesn't push product. Have a look at this thread I started. No pushing product and no cure-all there. Also, I am telling you to get free software and an old laptop... that is pushing nothing new. OK, I am pushing you to get a cable, but if you research you can build your own. It is hardly worth it though when you consider the time it will take versus the price to just buy one.

YOU DO!!!!! An old laptop, free software, and a cable and you are good to go!

Not at all. Where did you read that?

TunerPro RT and WinALDL are both free. TunerPro requires a bit more work to set up, but also provides more features. WinALDL is pretty much plug and play once you find your COM port and your baud rate. Which is super easy. I set both up by doing some web searches and downloading some files. I had been out of the TPI game for about 18 years and was able to find all of this super easy. As Tuned suggested, I am using a MOATES cable and an old lap top with TunerPro RT/WinALDL. Cost me about $100 to get all set up.


It is an 86, I asked above.