Another 5.7 TPI idle issue 1990 IROC Z
Thread Starter
Junior Member
Joined: Feb 2019
Posts: 2
Likes: 0
Another 5.7 TPI idle issue 1990 IROC Z
Hey guys new to the forums but not to the car world. Before you say use the search function, please know I have read everything I can on the issue and I'm beyond frustrated. I have a 90 Iroc 5.7 L98. I am having idle issues. The car cold starts and hot starts great. It revs to the moon without hesitation. The car has a small surge at idle and occasionally stalls when i put the car in reverse. It is totally random. I just finished restoring this car, and it is a 70k original mile car. I need to replace the tach board so its hard to tell what it is actually idling at. Sometimes it has a surge to it and sometimes it the car seems to idle a little high. Other times it seems to be fine. I don't get it. The idle tends to climb a bit when on the brake, so I'm not sure if there is a small vacuum leak somewhere.
So far i have replaced and set the TPS to 5.4.
Installed a new IAC
Installed a new MAP
Installed a new CTS (This seems to help out with the stalling. It originally seemed to have a miss as well but this seemed to clear that up a bit)
Installed new cap and rotor
Installed new plugs
Installed new pump and filter
Sprayed with carb cleaner for vac leaks as well as cleaned the throttle body
All injectors ohmed out at 16
Other than this idle issue the car seems to run great. Starts great hot and cold, and idles up fine when your on the gas. Seems to run great when put in drive, however sometimes the car just wants to die when you put it in gear. Im stumped, any ideas. I restore cars for a living, this car was built to sell and its a beautiful original car, I just don't want to sell it until i know its right.
So far i have replaced and set the TPS to 5.4.
Installed a new IAC
Installed a new MAP
Installed a new CTS (This seems to help out with the stalling. It originally seemed to have a miss as well but this seemed to clear that up a bit)
Installed new cap and rotor
Installed new plugs
Installed new pump and filter
Sprayed with carb cleaner for vac leaks as well as cleaned the throttle body
All injectors ohmed out at 16
Other than this idle issue the car seems to run great. Starts great hot and cold, and idles up fine when your on the gas. Seems to run great when put in drive, however sometimes the car just wants to die when you put it in gear. Im stumped, any ideas. I restore cars for a living, this car was built to sell and its a beautiful original car, I just don't want to sell it until i know its right.
Joined: Dec 2004
Posts: 16,737
Likes: 994
From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: Another 5.7 TPI idle issue 1990 IROC Z
The spec for the tps is .67-.76 on speed density tpi. Have you tried a new icm ?
The stock injectors suck for this car multecs coils short out. Are your readings hot ?
The stock injectors suck for this car multecs coils short out. Are your readings hot ?
Junior Member
Joined: Oct 2012
Posts: 69
Likes: 6
From: canada ontario mississauga
Car: 1985 trans am/ 1991 RS
Engine: 355sbc/ v6
Transmission: 700r4 automatic
Re: Another 5.7 TPI idle issue 1990 IROC Z
I don't know much but do you think the torque converter may be your problem?
Joined: Aug 2009
Posts: 1,972
Likes: 127
From: Los Angeles
Car: 1989 IROC Convertible
Engine: 350 TPI L98
Transmission: WC T5
Axle/Gears: 3.42
Re: Another 5.7 TPI idle issue 1990 IROC Z
I wouldn't touch the Multec injectors- yet. If you go to Bosch D3 or other you will need a custom tune- which may help anyway.
Did you spray the outside of the intake system for leaks?
Did you read ohms to ground from the engine block/heads/intake locations? This will check your grounds.
Did you spray the outside of the intake system for leaks?
Did you read ohms to ground from the engine block/heads/intake locations? This will check your grounds.
Joined: Oct 2001
Posts: 12,213
Likes: 1,140
From: Il
Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Another 5.7 TPI idle issue 1990 IROC Z
Brake booster have a leak?
Joined: Dec 2004
Posts: 16,737
Likes: 994
From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
worth looking into blocking the line to the booster if you can duplicate the issue. Sounds real random the worst drive ability issues to find.Trending Topics
Thread Starter
Junior Member
Joined: Feb 2019
Posts: 2
Likes: 0
Re: Another 5.7 TPI idle issue 1990 IROC Z
Ya I don’t get it, I have seemed to fix the stall when but in gear with the temp sensor. From what I see it is happening once it goes into closed loop. I reset the TPS to around .69. The weird thing is once it’s in drive or reverse it sits and idles great. Once it’s back to park it’s starts surging again and idles a bit high. I cant believe it’s the injectors, it would stumble and search all the time. I’m going to drop a new distributor in it tommorrow and reset the timing, but I’m not that hopeful at this point.
Joined: Aug 2009
Posts: 1,972
Likes: 127
From: Los Angeles
Car: 1989 IROC Convertible
Engine: 350 TPI L98
Transmission: WC T5
Axle/Gears: 3.42
Re: Another 5.7 TPI idle issue 1990 IROC Z
Is your base timing rock steady or does it wander?
Senior Member
iTrader: (4)
Joined: Mar 2004
Posts: 813
Likes: 1
From: San Antonio, Tx
Car: 86 Camaro Z28/ 87 Camaro IROC Z28
Engine: 5.0L TPI LB9 / 5.0 TPI LB9 w/cam
Transmission: Built 700R4 with Transgo shift kit
Axle/Gears: 3.27 9 bolt Posi/ 2.73 10 bolt Posi
Re: Another 5.7 TPI idle issue 1990 IROC Z
Have you set the minimum air for the idle? You messed with the IAC and TPS. Minimum air is pretty important. What brand of TPS did you buy?
Also, pull the vacuum line for the fuel pressure regulator and smell it for gas.
Also, pull the vacuum line for the fuel pressure regulator and smell it for gas.
Joined: Mar 2017
Posts: 4,255
Likes: 427
From: Portland, OR
Car: 86 Imponte Ruiner 450GT, 91 Formula
Engine: 350 Vortec, FIRST TPI, 325 RWHP
Transmission: 700R4 3000 stall.
Axle/Gears: 9 Bolt Torsen 3.70
Re: Another 5.7 TPI idle issue 1990 IROC Z
Why don't you check BLM's at idle? O2 sensor switching properly?
GD
GD
Thread
Thread Starter
Forum
Replies
Last Post
W.E.G.
Tech / General Engine
0
Aug 20, 2017 09:50 AM
Zach/90\irocZ
Tech / General Engine
19
Dec 22, 2012 09:35 PM