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1988 Alfa Romeo Graduate
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Discussion Starter #1
This new to me 1988 Graduate has been very jerky going from a still position after going into 1st gear. You simply must feather the gas pedal and slowly pick up speed. If you don't, such as go 1/2 throttle, it violently jerks and struggles and you have to put the clutch back in. This happened only once when I test drove the car before I bought it, and I was willing to overlook it. Now it is common whenever engine is warm.

In working it up, and I believe that the TPS is defective. At idle, pins 2 and 18 is zero ohms, and is open between 3 and 18. As you advance the throttle, you here the CLICK and pins 2 and 18 become open. BUT, pins 3 and 18 never close to 0 ohms, in fact it is fully open. I never could rotate the switch to get the open throttle contacts to engage. I took it off and confirmed the lack of 3 and 18 never went to 0 ohms. Since it was dead, I drilled a small hole in the bottom and sprayed in some contact cleaner. Shook it and worked the movement for about an hour. Interestingly, when tested on the bench there were now 3 positions: typical idle, after a 1/4 turn no contacts were closed anywhere on switch, and after another 1/4 turn there was contact as expected between 3 and 18. But it was sort of intermittent. So question #1, is this just a 2 state switch or a 3 state switch? Regardless, the intermittent nature even near full throttle makes it defective, but I would like to know if there a mid range state?

Question #2, I actually see that these are not trivial to buy. On ebay is see several used Bosch. Only one is the same as my part number which is 0280120304, at $64. I see some 300's , 302s, and 303s, too. I can't find them at Centerline. Vicks says theirs is for 1989-on and mine is a 1988, and while they show a Bosch part in the picture, underneath it says its an alternative. CarID has two new ones, made by Standard ($89) and Walker Products ($64). So, my preference would be Bosch new, but they do't seem to be around. Would you go with used Bosch or new alternative brand? (also, are the 300, 302, 304s actually different?)

steve
 

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old toyotas and datsuns/nissans used L-jet..perhaps you can look there?
 

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I would stick with the Bosch 0 280 120 304 TPS, but in my experience, these units are prone to failure.

The one on my '88 was faulty when I purchased the car in 2014. I discovered this by testing the resistance across the terminals as you have done.

I bought a used 0 280 120 304 off of eBay and it too proved unusable, but only because I could not get it mounted on the throttle body so that it was clocked to "click" in the proper throttle positions.

I found another one in the Forum classifieds (same Bosch part number) that was being offered by a member (for $30 IIRC). That one produced acceptable resistance readings and could be mounted to "click" at the correct times.

In conclusion, there are good used ones out there, but you may have to hunt and take a couple of chances before you find one that works.
 

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1988 Alfa Romeo Graduate
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Discussion Starter #4
I would stick with the Bosch 0 280 120 304 TPS, but in my experience, these units are prone to failure.

The one on my '88 was faulty when I purchased the car in 2014. I discovered this by testing the resistance across the terminals as you have done.

I bought a used 0 280 120 304 off of eBay and it too proved unusable, but only because I could not get it mounted on the throttle body so that it was clocked to "click" in the proper throttle positions.

I found another one in the Forum classifieds (same Bosch part number) that was being offered by a member (for $30 IIRC). That one produced acceptable resistance readings and could be mounted to "click" at the correct times.

In conclusion, there are good used ones out there, but you may have to hunt and take a couple of chances before you find one that works.

So you are not in favor of the new replacements? Do you think that they are not durable, poorly made, don't work from the box?

Also, is there a space "not idle, not full throttle" where all the pins are disconnected? What does that cause the system to do in that middle portion? "Some" advancement? "Some" enrichment? Still not clear on that.
 

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If you take one apart. It's just 2 on/ off switchs one for idle, am one for **** the torpedoes. I am flooring it
 

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The TPS is not a potentiometer. As stated above it is an on - off switch that tells the ECU three things. Is the throttle closed, is the throttle not closed, is the throttle fully open.
 
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Since it does work at full closed position, I do not think that is your problem. It will affect the VVT solenoid function at high RPMs causing it not to engage.
Again, this is a switch so the ECU knows if you are at idle, in between idle and WOT and at WOT.
You may want to adjust it so that it does not show closed between 2 and 18 until the throttle is indeed fully closed.
The TPS should not change until 1990 when they went to Motronic injection.
As long as the form factor on replacements is the same and the functionality between contacts the same, it will work.
I have interchanged between Porsche and Alfa without issues as some Porsche models use that switch.
 

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Rock Auto has two different ones listed. Walker, and Standard Motor Products. $66. and $82.
 

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I'm trying to figure out the relationship between a faulty TPS & the take off judder.
You simply must feather the gas pedal and slowly pick up speed.
I'd suggest checking the motor mounts & transmission mount. Faulty motor mounts will allow the engine to move beyond the designed limits & this would be more pronounced when taking off from a stop. In addition, this excessive engine movement will cause strain to the joints in the big air duct across the top of the motor. It is common to find a split in the accordion section of the air duct near the Air Flow Meter. At rest this split might be closed but as the engine moves the split opens. The resulting intake air leak causes the flap in the AFM to close cutting off fuel injection. The engine moves back, the split closes, the flap responds and fuel is delivered, the engine rocks again, etc., etc.
 

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I agree with Eric that this does not sound like a TPS issue. Check for leaks as he mentioned.
I assume that it idles fine?
Does it do this both hot and cold?
 

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Discussion Starter #12
The TPS is not a potentiometer. As stated above it is an on - off switch that tells the ECU three things. Is the throttle closed, is the throttle not closed, is the throttle fully open.
REPIES TO ALL:

Thank you for your input. I do not think anyone said that it was a potentiometer. Rather I asked if it had 3 states, and, what the terminal connections were for each of the 3 states. We know the ones for idle and full throttle. So what are the connections at "throttle is neither closed or open"?

I will check for that split. At least at idle, when I take off the oil breather cap, the engine idle drops way down and it almost dies so I feel that in this static state there are not much in the way of air leaks.

So, in the L-jet, is there anything that gives you extra torque from coasting at 900 rpm to say 2500 rpm as you are try to accelerate? That is where the problem is.

I does not happen when cold. Takes about 5 min of driving to start happening.

I will reset it to the idle setting where it is correct, and for the time being ignore the fact that there is no wide-open throttle connection.

I will also look at motor and transmission mounts.

Steve
 

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yes, I'd forget the TPS...set it to click the moment it is just off idle and be done with it.

to get back to the problem you are experiencing:
if I understand correct, you cannot take off from a standstill smoothly WHEN the engine is warm (iow cold there is no problem to accelerate smoothly)....?
You have to basically give it at least half throttle to move off anywhere...when warm
that correct?

does the car idle normally when warm?
when in neutral and you accelerate, does it rev up normally, smoothly when warm?
 

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:

We know the ones for idle and full throttle. So what are the connections at "throttle is neither closed or open"?

I will check for that split. At least at idle, when I take off the oil breather cap, the engine idle drops way down and it almost dies so I feel that in this static state there are not much in the way of air leaks.

So, in the L-jet, is there anything that gives you extra torque from coasting at 900 rpm to say 2500 rpm as you are try to accelerate? That is where the problem is.

I does not happen when cold. Takes about 5 min of driving to start happening.

I will reset it to the idle setting where it is correct, and for the time being ignore the fact that there is no wide-open throttle connection.

I will also look at motor and transmission mounts.

Steve
[/QUOTE]
Well the 3 states are as previously explained. When it is neither open nor closed, there is no contact closure to the ECU.
Nothing gives extra torque between 900 and 2500 RPM.
The only thing that helps performance is the VVT solenoid at WOT and above 4000 RPM.
Oil breather cap was a good test and it did what it should have done. Same should happen if you lift up the dip stick.
Agreed about not worrying about the WOT connection for now. You can drive all the time and never need it if you don't floor it.
If you are already moving and you shift from say 1st to 2nd and are at low RPM after shifting, does it respond properly?

Just asking whatever pops into my head as you have a real enigma here so far.

Wish you were closer so we could check it out. I love a good challenge
 

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1987 Alfa Romeo Spider Quadrifoglio
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This new to me 1988 Graduate has been very jerky going from a still position after going into 1st gear. You simply must feather the gas pedal and slowly pick up speed. If you don't, such as go 1/2 throttle, it violently jerks and struggles and you have to put the clutch back in. This happened only once when I test drove the car before I bought it, and I was willing to overlook it. Now it is common whenever engine is warm.

In working it up, and I believe that the TPS is defective. At idle, pins 2 and 18 is zero ohms, and is open between 3 and 18. As you advance the throttle, you here the CLICK and pins 2 and 18 become open. BUT, pins 3 and 18 never close to 0 ohms, in fact it is fully open. I never could rotate the switch to get the open throttle contacts to engage. I took it off and confirmed the lack of 3 and 18 never went to 0 ohms. Since it was dead, I drilled a small hole in the bottom and sprayed in some contact cleaner. Shook it and worked the movement for about an hour. Interestingly, when tested on the bench there were now 3 positions: typical idle, after a 1/4 turn no contacts were closed anywhere on switch, and after another 1/4 turn there was contact as expected between 3 and 18. But it was sort of intermittent. So question #1, is this just a 2 state switch or a 3 state switch? Regardless, the intermittent nature even near full throttle makes it defective, but I would like to know if there a mid range state?

Question #2, I actually see that these are not trivial to buy. On ebay is see several used Bosch. Only one is the same as my part number which is 0280120304, at $64. I see some 300's , 302s, and 303s, too. I can't find them at Centerline. Vicks says theirs is for 1989-on and mine is a 1988, and while they show a Bosch part in the picture, underneath it says its an alternative. CarID has two new ones, made by Standard ($89) and Walker Products ($64). So, my preference would be Bosch new, but they do't seem to be around. Would you go with used Bosch or new alternative brand? (also, are the 300, 302, 304s actually different?)

steve
I replaced mine with one from Rockauto; made by Standard Auto Products ....works perfectly, for $80.
 

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From the Alfa shop manual:
1670957

1670959


Connect your ohm meter to terminals #18 & #2 = no resistance at idle. Connect to terminals #18 #3 = no resistance at full throttle. In between (part throttle) no connections between any terminals.
 

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1987 Alfa Romeo Spider Quadrifoglio
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yes, I'd forget the TPS...set it to click the moment it is just off idle and be done with it.

to get back to the problem you are experiencing:
if I understand correct, you cannot take off from a standstill smoothly WHEN the engine is warm (iow cold there is no problem to accelerate smoothly)....?
You have to basically give it at least half throttle to move off anywhere...when warm
that correct?

does the car idle normally when warm?
when in neutral and you accelerate, does it rev up normally, smoothly when warm?
It might be worth it to electrically test/inspect both temperature coolant sensors...the fuel injection sensor, but maybe even more importantly the one for the ignition. As the engine warms and that sensor is sending erroneous signals to the ignition module, the engine timing could be suffering; could be very retarded when trying to accelerate. Just a thought....
 

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Discussion Starter #18
From the Alfa shop manual:
View attachment 1670957
View attachment 1670959

Connect your ohm meter to terminals #18 & #2 = no resistance at idle. Connect to terminals #18 #3 = no resistance at full throttle. In between (part throttle) no connections between any terminals.
Thank you. You are the first to answer this question fully about the "in between position". And as I indicated I have performed this test. I never get the full throttle connection, but that would not explain my issue now that I finally know what the intermediate connections are supposed to be, because that is where the throttle is during the jerking. I have a few things that I did yesterday (several at once, always hard to know what helps). See below. Thank you.

steve
 

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Thank you. You are the first to answer this question fully about the "in between position". And as I indicated I have performed this test. I never get the full throttle connection, but that would not explain my issue now that I finally know what the intermediate connections are supposed to be, because that is where the throttle is during the jerking. I have a few things that I did yesterday (several at once, always hard to know what helps). See below. Thank you.

steve
Steve
I saw a "see below" regarding several things that you did yesterday but did not see anything.
What did you try yesterday?
Thanks
 

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Discussion Starter #20
It might be worth it to electrically test/inspect both temperature coolant sensors...the fuel injection sensor, but maybe even more importantly the one for the ignition. As the engine warms and that sensor is sending erroneous signals to the ignition module, the engine timing could be suffering; could be very retarded when trying to accelerate. Just a thought....
You may be on to something. Yesterday I cleaned the intake. The flapper in the AFM was nice and moved easily. It was 3/8ths inch open when cold, ignition off. At the other end, that flapper seemed a little dirty so it was cleaned and required less force to move it when done. It seems nearly fully closed at idle, and goes horizontal (fully open) at wide open throttle.

I then noticed that the male connector to one of the sensors at the firewall was crumbling. It is the one that goes to the black female connector on the harness. I pulled the housing off and the 3 pins (a shielded cable and its ground, and a black/yellow wire I believe) and the soldering/crimping were unscathed. So, I plugged them in and secured it temporarily. Then I remembered that the PO used high octane gas because he said it "ran better". So I boosted the octane.

Last night it ran quite nicely, hot or cold, from a dead stop through the badlands.

I have ordered the TPS, and a new male connector from EFI connectors.info
Thank you,

steve
 
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