So i started having an issue with my 87 iroc 5.7 tpi ive been searching for a week now and nothing quite like my problem.

so here it is.

If im idleing in park and i punch the throttle. it shoots to about 1200-1500rpm then seems to pause for a berif second then continues.

this all came about because i use to be able to just punch the throttle from a stop light or around a corner and the tires would light like crazy. and now it hardly squeals them.

but it still hauls *** about 1800 or so.

one thing i know for sure is that if i have a timing light on the mark idleing. and i have somone punch it the timing drops fromthe 20's?(the first advance with est plugged in) right down to about 12 then goes up to the 30's

so it seems like something it makeing my timing dip down before advancing. which im pretty sure is my problem.

heres a list of new parts and things ive tested.
cap, rotor, the whole dist, plugs(ac delco) maf, bosch III injestors. coil,

ive checked, tps .54v 4.5+ at wot, no dead spots, timing(ive tryed several different spots all have the same result of my problem. checked for an intake leeks,fuel leeks,

fuel pressure is 42-43 engien off key on

39 idleing

and wot it rapidly swings from 40-48(like the needle is a blurr)

no check engine light what soever.

car seems maybe? just a little rich.

idle seems to shake more then it should.

anyways any help would be apriciated.

ill let you know if ive typed it or what not.

 

A bad or dying MAF will cause a timing issue.

I believe what you are seeing is normal though. This table is an extreme case as its from a TBI truck and its in my TPI ECM but it gets the point across more easily. See the flat platue on the left bottem where the engine idles at about 600 rpm/40 KPA. Now smack the throttle, the engine is still at 600 rpm, but the MAP shoots up toward 100 KPA. The spark lookup cell is shifted to the bottem right, into the valley. Then as the throttle is held open the RPMs rise but the MAP stays near 100 KPA and the spark lookup cell is taken up along the right hand side. Now when the engine is good and tached up and you lift from the throttle, the lookup cell shifts from the right back to the left as the vacuum builds back up. The lookup cell will end up near the top left and then as the rpm drops back down with the throttle plates closed it will shift back down toward the idle rpm / MAP.

 

ok i c what you talking about. but im not quite sure how to relate it to my timming jumping down before going up. as far as i know and have experienced timing should go upat wot.

also from that table to me it looks like the rpms would increase rapidly and stedily in the lower rpms 800-3000

where as mine litterly vroom-1200hesitation/pause-1500-and vroom

and ive never seen that on these cars and i myself have owned several.

and it does it consistanly never fails.

thanks tho. im still trying to make out that table but for the most part i think i get it. i just dont see where it wouldmake the engine pause or hesitate acceleration at 1500ish.

 

some more info for you guys.

i was messing with relays today and i can literly unplug ever relay under hood and the car will run the same. no cel. even the fuel pump relay the car still stays runnin and will start up with it unplugged too.

i do get a code 33 with the maf power relay unplugged.

but its just weird to me that no other relay has any affect.

also esc modual? any possible relation to my problem?

car seems to run rich. smells of fuel out of exuast.

i also just changed out my week old delco plugs for another set of delcos just ti make sure i didnt get a shitty plug still the same.

keep any advise comming. this problem is irriateing me. it really has a nice pause going on right at 1500. deffinayl not normal at all.

 

one of my ta's would just kinda give up at about 3 grand if i was really on the gas... turned out to be a plugged cat. how old is ur cat?

 

glad you asked. catless exhaust.

what buggs me is once i figure this out its going to be something so small. haha

well thanks and keep them comming.

 

MAYBE YOU HAVE 20 YR OLD INJECTORS THAT ARE FINALLY GIVING OUT,, OR CLOGGED ONES.

 

You sure you unplugged the fuel pump relay and car still ran? That is impossible for it to happen since you break off the power supply to the fuel pump.

Try idling in park with the foot on the brake pedal and see if it still does what it is doing.

 

brand new injectors bosch design 3 installed 1 week ago

im 100% aure i unplugged the fuel pump relay and it still ran

if i unplug the fuel pump fuse it dies right away but not the relay.

ill try the brake thing. what would this simulate exactly?

 

couple other things that just popped into my head that i hzve tryed. i did a compression test and was very happy to see 151-152 on all 8.

i replaced the CTS when i first ot the car because the old one had a code.

i unplugged the knock sensor with the same results. and got no code?

am i supposed to get a code with knock sensor unplugged?

one thing i havent really check in my pcv valve. i mean i took it out and shook it and it rattles. but are their any other tests i can do to make sure its not sucking to much air at idle maybe?

 

PCV won't effect the idle even if it was bad. The IAC will open or close to compensate. What will effect the idle is ANY un-metere air leaking into the intake tract that the MAF does not see. This includes leaking engine gaskets that might be drawing in air. I've seen OBDII GM Vehicles give "system too lean codes" and exhibit poor running through something as simple as leaving the oil cap off or loose. Check for those un-metered air leaks.

 

yea. ive heard of that before ill check.

and reporting on checking the condition with the brake pedal depressed its the same.

im aure its running rich tho not lean its has a very gas filled exaust. that it didnt have before the problem came about.

i really feel that its something to do with timing or spark. it feels like a consistant random miss. but literly every component is new on the ignition system. exsept esc modual

well keep them coming. im an automotive tech and im stumped. even our lead tech has run out of ideas.

its going to be one of those problems.

 

this might be along shot, and a pain in the *** but, rounded off cam lobe?

 

yea its a possibility. but i had a rounded off cam lobe on an s10 with a v8 i had and it reved fine just didnt have power.

but i am planning on takeing off my valve covers and ill run the car with them off and check for any rocker that has less up and down movment then the others.

 

so some more information.

my car is starting to feel more and more like ****. felt uber slow today. and cold start idle is at like 500 now then progressivly goes up to 1100ish? wtf? its supposed to be pretty much oppisite.

i hooke the the fuel pressure gauge and idle is now at 30psi less then a week ago it was at 39.

wot is at 38psi i hooked it up while driving. and 1/4-3/4 throttle the needle bounces so fast between 30 and 45 that you can hardly see the damn thing. and the injectors seem to be very loud while it bounces like that.

im almost feeling liek the problem is the mid grade cheveron i put in it the night i got done with the mods becuase it felt so much better after i didnt the inejctors msd coil plugs wires cap rotor.

it almost seems like its went downhill since that fill up. but im at 1/4 tank so ill be filling up shell this next time to see if their is any difference

im also going to pull my brand new fuel filter tommorw and see if its allready plugeed if it is i think cheveron might be to blame?

sounds legit?

or my fuel pump is saying hey f**k you ahaha

man. this problem is drivng me nuts.

 

thats wierd stuff. i gues there is a chance it was bad gas u put in. i dont have experince with bad gas, all i know is it likes to take out fuel pumps, filters, injectors.

but mabey ur fuel pump is on the way out. how old is it? i dont understand why it would idle the way it is though if it was ur pump. any pinched hard fuel lines?

wish i could be of more help to u.

 

well today i filled up with a differnt gas shells v- power and no major change in performance. so i dont think bad gass is the cause.

one thing i did find out it rained today and i can barly spin the damn tires wet.

something is deffinayl worng.

i hooked up a otc scantool today and all the readings seem to be ok.

blm was at 108 at one point at idle then one time it was 128 at idle then sometimes it was 130's at idle it seemed to vary every time i hooked the otc up.

the i installed a new o2 sensor and had my new maf warrented out just in case and bought new relays for maf power and puel pump.

same no change at all.

but now the otc scanner will only connect when cold as soon ad the engine is running and warmed up it wont connect with my pc. what the hell.

and as far as pinched fuel lines i havent seen any. but i know that 30psi at idle is low and 38 at wot is low.

and i dont know what to thing at part throttle it deffinaly should not be fluxuating like that.

michell repair states that a fuel pressure opf 24 at idle most likely wouldnt alow the car to stay idleing.

so it very well may be that the fuel pump is takeing a crap on me.

ill have to do some more testing on it tho before i drop that tank. i did one in one of my birds and its no fun job.

keep the responses comming. ill keep updateing with new info and things ive tryed.

 

alright more information.

today i started it up cold and man it surged from 500 to 1200 about 3 really rough surgest an then settled down at 1100 untill warmed up.

then after work it did the same thing but this time when i gave ti gas it backfired several times then leveled out and te car seemed to stumble off throttle untill it was warm.

theres something new everday. i honesly wish the car would ust stop running im sure it would be much easyer to pinpoint the problem then. or something.

anyways im going to test some more stuff and restest other stuff tonight then i have all day tomorow no work and ill keep plugging away.

 

symtoms: no power, bad idle, backfire... By any chance did you adjust valves lately?.. rally might be mechanical.. are you sure base timing is correct? are plug wires crossed? check them .. also is ign. module good. and is the distrubuter shaft have no play under the cap.. if it wobbles the dist. is NG

 

i have not ajusted the valves lately. they are hydaulic right? ajust with engine running?

i am planning on pulling the valve covers off tommorw tho and checking for broken springs, bent rods, or a valve with minimal movment for worn cam lobe.

ignition timing is at 8* btdc

dist shaf,modual, pickup coil, ign coil are all new and good.

well i knwo the big thing about 5 and 7 wires being to close but seperating them and keeping them togeth has no change in condition and no plug wires are crossed it runs on a solid 8 just slightly rough and im not feeling the power.

i also compression tested all 8 are 150

vacumm is still at 22hg idle nice and steady and drops to 0 at wot

thanks again. keep them comming

 

https://www.thirdgen.org/forums/tpi/...ght=hesitation

i found this thread searching today and the guy actually has a video of the exact thing im getting. listen carfully and you will see how the engine seems to pause.

vadar replyed to the post as it being normal. but it really seems like it wasent like that before.

and im still wondering about my timing. when you punch the gas and watch the timing mark it goes retards to like 12-14 then shoots back up to total timing.

ive seen a couple posts on this aswell but no answers or verifications that thats notmal.

if any of you tpi guys could go hook up a light to your car and have a buddy stab it off idle and see what your timing does it would be apreciated.

oh and a side note. i went checking stuff last night everything was the same as before. and then all the sudden the car came back to life it still hs the hesitation but it felt much smoother at idle and just seemed better over all.

but i still feel with 3.45 gears i should be spinning tires off the line if i goose it.

 

when you check the fuel preasure take the vac line off while it is running and the presure sould drop approx 10 psi

what does the signal wire to the tps show while running if its jumping around replace the tps

no vac leaks right

wiggle the throttle shaft on the throttlebody

take out Iac put it in a wal mart bag pugged up and turn the key

if the rod pops out its good if not replace

put a noid light on each of the injectors

 

im assuming for the fuel pressure your backwards. it should go up aprox 10psi with no vac on regulator.

which it does but it goes from 30 to 39 kinda low

no vac leeks.

throttle leaver is tight

iac is one thing i need to check still
altho when i had the OTC hooked up the iac started high on startup and worked its way down but at hot idle it was around 10 or so which i beleave is to low and might be letting in to much air?

and tps is steady .54 at idle no fluxuation and no dead spots.

noid light to check for power at each injector?

thanks
keep emm coming

that videos is the EXACT same thing my car is doing.

 

sorry about the 10 psi thing

I make mistakes

noid light would tell you if you have a pulsing ground

 

no problem. everyone does it.

yea i will try that.

i installed an egr blockoff plate today and put my holly afpr back in.

seems to to running fine and dandy right now. well since yesterday it seems to have been running better and i have no clue what made it change. but it still has the same hesitation. as in the video.

im just wondering how normal is that heasitation.

and typicaly how smooth is the idle in out 350 tpi auto cars? in gear and in park?

im feeling fairly confident that shes back and going stong again.

i would still like to get a prom and computer and see if their are any differences at all.

and one thing i was researching is heater o2 sensors with headers.

i have the hooker super comp shortie headers with the stock style 1 wire o2.

would this have any affects? maybe maybe not?

 

my car has NO hesitation and I would go to the ends of the earth to get rid of it like you are if I had one so dont give up

who burnt your prom?

 

i dont even know if the prom is stock or burnt im not sure. i know that the computer itself is a reman unit tho.

i would really like to find somone with a prom and computer so i could buy it or use it and see if their is any difference.

 

my car has done that since new. I just figured it was some computer delay... by the time it figured out the TPS voltage was rising, the MAF voltage changing, and then increasing the injector rate... all takes time, which results in that slight hesitation...

mine is a T5, so it doesn't bother me..

 

yea ive heard its normal and then people that say its not normal at all.

yea with a manual i wouldnt care at all. but with and auto its not working with me haha.

6 speed conversion soon tho. i have to pay for some school before i can put any more into this car

anywas more opinions on if its normal ,not normal. if mine is excessive maybe?

all will be apriciated.

 

Ok back again.

so ive givent up on the hesitation issue as im running even better at the track still then last time. and alot of peope have claimed it to be normal.

but the idle is rough i mean likt shakes the steering wheel and mirrors.

its driving me crazy but its perctly smooth at throttle or driving. and even seems to smooth out very slightly in gear but still shakes stuff.

as you may have see from the prior posts ive dont and checked almost everything on this car.

so im stumped and need some new ideas.

EGR is now blocked off aswell.

min air and tps are set also with a new iac installed.

thanks. im going crazy here.

 

My cars shakes as well not as bad as what u describe. did u replace ur motor mounts with polyurothane? a buddy of mine put polyurothane bushings in his talon and it shakes like a mad bitch.

 

i put poly motor mount bushing in my 89 i had and it didnt shake as bad as this but not they are the rubber bushings. ive visually lookked at them to see if they are slip or cracked but i havent actually put my hands on them and pryed on them to see if it has a busted bushing i supose that could cause exsessive shakeing.

thanks! any other things keep em coming. it has to be something.

 

sorry I really don't think this is normal at all I have an 87 350 auto car with only headers and exhaust and pulleys and mine doesn't do it at all but my 90 350 auto car is starting to do it. so please don't give up I will try and find more info for you, and oh yeah my fuel pressure on my 90 is 35 with the line plugged in and 45 with it unplugged and some one told me that is even bad .....

 

FYI, the above statement is false. The pump will run by the oil pressure switch (even with relay unplugged) once your oil pressure gets above 6psi. I checked it on my car.

I think you should check for vacuum leaks.

What's that module called behind the fuel pump relay that deals with spark advance?

 

The design III injectors will spray more fuel at idle, because the min injector value is 1.59 ms, in the stock arap 89 bin, and it needs lowered to 1.05 ms.

The battery volts are a lot less too for the design III. The injectors fix the lean at idle issue, and the ECM just adds more fuel trying to correct the same exact issue, so now you have too much fuel at idle. No egr and no cat will not help either. O2 swings are 100 mv higher (richer) with air pump blowing into manifolds.

My Car did the same thing with no egr and no cat with the design II injectors. After I retuned to the lower numbers, it got a lot better.

If it is running rich at idle, you are sooting up your new plugs and the O2 sensor. After driving at road speed they will clean out and the engine will run a lot better till it is idled again.

 

sorry i havent been on it a while i got a new truck and havent worked on the camaro.

UPDATE

well its still doing the same thing. but the ground on the driver side cylander head. well the ones that are suposed to bolt their. were not even bolted up.

so i bolted them up. it didnt change anything at all. why is this arnt those the ecm grounds?

shouldnt have those been effecting my car.'

also right in that same area as the ground their is a 2 prong weatherpack connector similar to the CTS connector. just sitting their coming off the main harness with no slack to go anywhere but right in the rear cylander head area.

what is this?

also im starting to notice my car will only downshift from 2nd to 1st at 12mph or less. but first runs out at like 35-40. 12mph seems a little low.

shifts into 3rd by 25-30 mph when driving "normal"

im not sure but any info will help im back on the case now.

also in regaurds to the transmission shifts. the kickdown is ajusted and the check valve is 100% open at wot.

just changed the trans filter and fluid with no change at all.

thanks guys the info is awesome.

and pandin. so what are you saying i need to do because i have the type 3 injectors?

 

Only if your Idle is way rich and can't be lowered. Like if you were idling at 1.60 ms and was too rich.

 

yea id need to hook up the scan tool and see where im at. but last time i hooked up the scan tool it would read untill it got warmed up then disconnect. haha.

anyways im very interested in why hookinh up those grounds didnt make any difference. they are ecm ground right?

and what the 2 prong connector is the same exact area of the drive side grounds is. its the same length as the ground wires coming off the same harness too.

like literly that connector cant go anywhere either something plugs into it right their or a longer wire plugs into it. ? i donno.

thanks